[XFS] Fix superblock validation regression for the zero imaxpct case.  Thanks to kjamieson for noticing.
[XFS] Fix superblock validation regression for the zero imaxpct case. 
Thanks to kjamieson for noticing.

SGI-PV: 951661
SGI-Modid: xfs-linux-melb:xfs-kern:25675a

Signed-off-by: Nathan Scott <e2e3f1f24cbc439f8c1ba9b08f9954237d64be64@sgi.com>

TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs