btrfs: fix incomplete parameter rename in btrfs_decompress()

Commit 2c25716 ("btrfs: zlib: fix and simplify the inline extent
decompression") renamed the 'start_byte' parameter to 'dest_pgoff' in
the btrfs_decompress(). The remaining 'start_byte' references are
inconsistent with the actual implementation and may cause confusion for
developers.

Ensure consistency between function declaration and implementation.

Signed-off-by: Zhen Ni <zhen.ni@easystack.cn>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

Author: nizhen-t

fs/btrfs/compression.c

@@ -1084,7 +1084,8 @@ static int btrfs_decompress_bio(struct compressed_bio *cb)
 /*
  * a less complex decompression routine.  Our compressed data fits in a
  * single page, and we want to read a single page out of it.
- * start_byte tells us the offset into the compressed data we're interested in
+ * dest_pgoff tells us the offset into the destination folio where we write the
+ * decompressed data.
  */
 int btrfs_decompress(int type, const u8 *data_in, struct folio *dest_folio,
 		     unsigned long dest_pgoff, size_t srclen, size_t destlen)

fs/btrfs/compression.h

@@ -95,7 +95,7 @@ int btrfs_compress_folios(unsigned int type, int level, struct btrfs_inode *inod
 			  u64 start, struct folio **folios, unsigned long *out_folios,
 			 unsigned long *total_in, unsigned long *total_out);
 int btrfs_decompress(int type, const u8 *data_in, struct folio *dest_folio,
-		     unsigned long start_byte, size_t srclen, size_t destlen);
+		     unsigned long dest_pgoff, size_t srclen, size_t destlen);
 int btrfs_decompress_buf2page(const char *buf, u32 buf_len,
 			      struct compressed_bio *cb, u32 decompressed);