linux: Fix function point cast on vDSO handling

There is no need to cast to avoid, both pointer already have the
expected type.

It fixes the clang -Wpointer-type-mismatch error:

../sysdeps/unix/sysv/linux/gettimeofday.c:43:6: error: pointer type mismatch ('int (*)(struct timeval *, void *)' and 'void *') [-Werror,-Wpointer-type-mismatch]
   41 | libc_ifunc (__gettimeofday,
      | ~~~~~~~~~~~~~~~~~~~~~~~~~~~
   42 |             GLRO(dl_vdso_gettimeofday) != NULL
      |             ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   43 |             ? VDSO_IFUNC_RET (GLRO(dl_vdso_gettimeofday))
      |             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   44 |             : (void*) __gettimeofday_syscall)
      |             ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
./../include/libc-symbols.h:789:53: note: expanded from macro 'libc_ifunc'
  789 | #define libc_ifunc(name, expr) __ifunc (name, name, expr, void, INIT_ARCH)
      |                                ~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~
./../include/libc-symbols.h:705:34: note: expanded from macro '__ifunc'
  705 |   __ifunc_args (type_name, name, expr, init, arg)
      |   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~
./../include/libc-symbols.h:677:38: note: expanded from macro '__ifunc_args'
  677 |   __ifunc_resolver (type_name, name, expr, init, static, __VA_ARGS__);  \
      |   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
./../include/libc-symbols.h:667:33: note: expanded from macro '__ifunc_resolver'
  667 |     __typeof (type_name) *res = expr;                                   \
      |                                 ^~~~

Reviewed-by: Sam James <sam@gentoo.org>

sysdeps/unix/sysv/linux/gettimeofday.c

@@ -41,7 +41,7 @@ __gettimeofday_syscall (struct timeval *restrict tv, void *restrict tz)
 libc_ifunc (__gettimeofday,
 	    GLRO(dl_vdso_gettimeofday) != NULL
 	    ? VDSO_IFUNC_RET (GLRO(dl_vdso_gettimeofday))
-	    : (void *) __gettimeofday_syscall)
+	    : __gettimeofday_syscall)
 
 # else
 int

sysdeps/unix/sysv/linux/powerpc/libc-vdso.h

@@ -47,7 +47,7 @@
   ({                                                     \
     static Elf64_FuncDesc vdso_opd = { .fd_toc = ~0x0 }; \
     vdso_opd.fd_func = (Elf64_Addr)value;                \
-    &vdso_opd;                                           \
+    (void *) &vdso_opd;                                  \
   })
 
 #else

sysdeps/unix/sysv/linux/time.c

@@ -36,7 +36,7 @@ time_syscall (time_t *t)
 # define INIT_ARCH()
 libc_ifunc (time,
 	    GLRO(dl_vdso_time) != NULL ? VDSO_IFUNC_RET (GLRO(dl_vdso_time))
-				       : (void *) time_syscall);
+				       : time_syscall);
 
 # else
 time_t