btrfs: Fix misspellings in comments.

Signed-off-by: Adam Buchbinder <adam.buchbinder@gmail.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/file.c

@@ -1847,7 +1847,7 @@ static ssize_t btrfs_file_write_iter(struct kiocb *iocb,
 	/*
 	 * We also have to set last_sub_trans to the current log transid,
 	 * otherwise subsequent syncs to a file that's been synced in this
-	 * transaction will appear to have already occured.
+	 * transaction will appear to have already occurred.
 	 */
 	spin_lock(&BTRFS_I(inode)->lock);
 	BTRFS_I(inode)->last_sub_trans = root->log_transid;