UBIFS: amend debugging inode size check function prototype

Add 'const struct ubifs_info *c' parameter to 'dbg_check_synced_i_size()'
function because we'll need it in the next patch when we switch to debugfs.
So this patch is just a preparation.

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>