jbd2: fix kernel-doc descriptions for jbd2_journal_shrink_{scan,count}()

jbd2: fix kernel-doc descriptions for jbd2_journal_shrink_{scan,count}()

Add the description of @shrink and @sc in jbd2_journal_shrink_scan() and
jbd2_journal_shrink_count() kernel-doc comment to remove warnings found
by running scripts/kernel-doc, which is caused by using 'make W=1'.
fs/jbd2/journal.c:1296: warning: Function parameter or member 'shrink'
not described in 'jbd2_journal_shrink_scan'
fs/jbd2/journal.c:1296: warning: Function parameter or member 'sc' not
described in 'jbd2_journal_shrink_scan'
fs/jbd2/journal.c:1320: warning: Function parameter or member 'shrink'
not described in 'jbd2_journal_shrink_count'
fs/jbd2/journal.c:1320: warning: Function parameter or member 'sc' not
described in 'jbd2_journal_shrink_count'

Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Yang Li <yang.lee@linux.alibaba.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20220110132841.34531-1-yang.lee@linux.alibaba.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>