ext4: fix incorrect function name in comment

Since commit 6b730a4 “ext4: hoist ext4_block_write_begin and
replace the __block_write_begin”, the comment should be updated
accordingly from "__block_write_begin" to "ext4_block_write_begin".

Fixes: 6b730a4 (“ext4: hoist ext4_block_write_begin and replace...")
Signed-off-by: Baolin Liu <liubaolin@kylinos.cn>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Link: https://patch.msgid.link/20250812021709.1120716-1-liubaolin12138@163.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

Author: murphy12138

fs/ext4/inode.c

@@ -3159,7 +3159,7 @@ static int ext4_da_write_begin(struct file *file, struct address_space *mapping,
 		folio_unlock(folio);
 		folio_put(folio);
 		/*
-		 * block_write_begin may have instantiated a few blocks
+		 * ext4_block_write_begin may have instantiated a few blocks
 		 * outside i_size.  Trim these off again. Don't need
 		 * i_size_read because we hold inode lock.
 		 */