btrfs: Call kunmap if zlib_inflateInit2 fails

If zlib_inflateInit2 fails, the input page is never unmapped.
Add a call to kunmap when it fails.
Signed-off-by: Nick Terrell <nickrterrell@gmail.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/zlib.c

@@ -250,6 +250,7 @@ static int zlib_decompress_biovec(struct list_head *ws, struct page **pages_in,
 
 	if (Z_OK != zlib_inflateInit2(&workspace->strm, wbits)) {
 		pr_warn("BTRFS: inflateInit failed\n");
+		kunmap(pages_in[page_in_index]);
 		return -EIO;
 	}
 	while (workspace->strm.total_in < srclen) {