syscall invocation.
* sysdeps/unix/sysv/linux/mips/pwrite64.c (__libc_pwrite64): Likewise.
* sysdeps/unix/sysv/linux/mips/pread.c (__libc_pread): Likewise.
Also, only assert off_t size is 4 for N32 and O32, and clean up
white space.
* sysdeps/unix/sysv/linux/mips/pwrite.c (__libc_pwrite): Likewise.