[SCSI] fnic: fix incorrect use of SLAB_CACHE_DMA flag

Driver was incorrectly using the SLAB_CACHE_DMA flag when creating a cache
for SGLs. fnic device does not have 24-bit DMA restrictions. Remove the flag
and allocations from ZONE_DMA.

Thanks to Roland Dreier and David Rientjes for pointing out the bug.

Signed-off-by: Abhijeet Joglekar <abjoglek@cisco.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>