xfs: remove unnecessary ternary from xfs_create

Since the "no-allocation" reservations for file creations has
been removed, the resblks value should be larger than zero, so
remove unnecessary ternary conditional.

Signed-off-by: Kaixu Xia <kaixuxia@tencent.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
[darrick: s/judgment/ternary/]
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>