btrfs: don't initialize 'offset' in map_private_extent_buffer()

In map_private_extent_buffer() the 'offset' variable is initialized to a
page aligned version of the 'start' parameter.

But later on it is overwritten with either the offset from the extent
buffer's start or 0.

So get rid of the initial initialization.

Reviewed-by: Nikolay Borisov <[email protected]>
Signed-off-by: Johannes Thumshirn <[email protected]>
Signed-off-by: David Sterba <[email protected]>

Author: Johannes Thumshirn

fs/btrfs/extent_io.c

@@ -5380,7 +5380,7 @@ int map_private_extent_buffer(const struct extent_buffer *eb,
 			      char **map, unsigned long *map_start,
 			      unsigned long *map_len)
 {
-	size_t offset = start & (PAGE_SIZE - 1);
+	size_t offset;
 	char *kaddr;
 	struct page *p;
 	size_t start_offset = eb->start & ((u64)PAGE_SIZE - 1);