xfs: cleanup quota check on disk blocks and inodes reservations

This patch is a cleanup of quota check on disk blocks and inodes
reservations, and changes it as follows.

(1) add a total_count variable to store the total number of
    current usages and new reservations for disk blocks and inodes,
    respectively.

(2) make it more readable to check if the local variables softlimit
    and hardlimit are positive. It has been changed as follows.
	    if (softlimit > 0ULL) -> if (softlimit)
	    if (hardlimit > 0ULL) -> if (hardlimit)
    This is because they are defined as xfs_qcnt_t which is unsigned.

Signed-off-by: Mitsuo Hayasaka <mitsuo.hayasaka.hu@hitachi.com>
Cc: Ben Myers <bpm@sgi.com>
Cc: Alex Elder <elder@kernel.org>
Cc: Christoph Hellwig <hch@lst.de>
Reviewed-by: Mark Tinguely <tinguely@sgi.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Ben Myers <bpm@sgi.com>