btrfs: fix argument list that the kdoc format and script verified

The warnings were found by running scripts/kernel-doc, which is
caused by using 'make W=1'.

fs/btrfs/extent_io.c:3210: warning: Function parameter or member
'bio_ctrl' not described in 'btrfs_bio_add_page'
fs/btrfs/extent_io.c:3210: warning: Excess function parameter 'bio'
description in 'btrfs_bio_add_page'
fs/btrfs/extent_io.c:3210: warning: Excess function parameter
'prev_bio_flags' description in 'btrfs_bio_add_page'
fs/btrfs/space-info.c:1602: warning: Excess function parameter 'root'
description in 'btrfs_reserve_metadata_bytes'
fs/btrfs/space-info.c:1602: warning: Function parameter or member
'fs_info' not described in 'btrfs_reserve_metadata_bytes'

Note: this is fixing only the warnings regarding parameter list, the
first line is not strictly conforming to the kdoc format as the btrfs
codebase does not stick to that and keeps the first line more free form
(because it's only for internal use).
Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Yang Li <yang.lee@linux.alibaba.com>
Reviewed-by: David Sterba <dsterba@suse.com>
[ add note ]
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/extent_io.c

@@ -3184,13 +3184,12 @@ struct bio *btrfs_bio_clone_partial(struct bio *orig, u64 offset, u64 size)
 /**
  * Attempt to add a page to bio
  *
- * @bio:	destination bio
+ * @bio_ctrl:	record both the bio, and its bio_flags
  * @page:	page to add to the bio
  * @disk_bytenr:  offset of the new bio or to check whether we are adding
  *                a contiguous page to the previous one
- * @pg_offset:	starting offset in the page
  * @size:	portion of page that we want to write
- * @prev_bio_flags:  flags of previous bio to see if we can merge the current one
+ * @pg_offset:	starting offset in the page
  * @bio_flags:	flags of the current bio to see if we can merge them
  *
  * Attempt to add a page to bio considering stripe alignment etc.

fs/btrfs/space-info.c

@@ -1588,7 +1588,7 @@ static int __reserve_bytes(struct btrfs_fs_info *fs_info,
 /**
  * Trye to reserve metadata bytes from the block_rsv's space
  *
- * @root:       the root we're allocating for
+ * @fs_info:    the filesystem
  * @block_rsv:  block_rsv we're allocating for
  * @orig_bytes: number of bytes we want
  * @flush:      whether or not we can flush to make our reservation