Fix more typos in comments.

Patch by CharSyam, plus a few more I spotted with grep.

src/backend/storage/buffer/bufmgr.c

@@ -2165,7 +2165,7 @@ CheckForBufferLeaks(void)
 		}
 	}
 
-	/* if neccessary search the hash */
+	/* if necessary search the hash */
 	if (PrivateRefCountOverflowed)
 	{
 		HASH_SEQ_STATUS hstat;

src/backend/storage/ipc/dsm.c

@@ -225,7 +225,7 @@ dsm_cleanup_using_control_segment(dsm_handle old_control_handle)
 	/*
 	 * Try to attach the segment.  If this fails, it probably just means that
 	 * the operating system has been rebooted and the segment no longer
-	 * exists, or an unrelated proces has used the same shm ID.  So just fall
+	 * exists, or an unrelated process has used the same shm ID.  So just fall
 	 * out quietly.
 	 */
 	if (!dsm_impl_op(DSM_OP_ATTACH, old_control_handle, 0, &impl_private,

src/backend/storage/ipc/procarray.c

@@ -2001,7 +2001,7 @@ GetOldestSafeDecodingTransactionId(void)
 	/*
 	 * If there's already a slot pegging the xmin horizon, we can start with
 	 * that value, it's guaranteed to be safe since it's computed by this
-	 * routine initally and has been enforced since.
+	 * routine initially and has been enforced since.
 	 */
 	if (TransactionIdIsValid(procArray->replication_slot_catalog_xmin) &&
 		TransactionIdPrecedes(procArray->replication_slot_catalog_xmin,

src/backend/storage/ipc/shm_mq.c

@@ -1047,7 +1047,7 @@ shm_mq_inc_bytes_read(volatile shm_mq *mq, Size n)
 
 /*
  * Get the number of bytes written.  The sender need not use this to access
- * the count of bytes written, but the reciever must.
+ * the count of bytes written, but the receiver must.
  */
 static uint64
 shm_mq_get_bytes_written(volatile shm_mq *mq, bool *detached)