btrfs: remove shadowing variables in __btrfs_buffered_write

There are lockstart and lockend defined in the function and not used
after their duplicate definition scope ends, it's safe to reuse them.

Signed-off-by: David Sterba <dsterba@suse.cz>

fs/btrfs/file.c

@@ -1631,8 +1631,8 @@ again:
 			btrfs_end_write_no_snapshoting(root);
 
 		if (only_release_metadata && copied > 0) {
-			u64 lockstart = round_down(pos, root->sectorsize);
-			u64 lockend = lockstart +
+			lockstart = round_down(pos, root->sectorsize);
+			lockend = lockstart +
 				(dirty_pages << PAGE_CACHE_SHIFT) - 1;
 
 			set_extent_bit(&BTRFS_I(inode)->io_tree, lockstart,