[SCSI] ibmvfc: Fix command timeouts due to cached CRQ access

The CRQs used by the ibmvfc driver are read and written by both
the client and the server. Therefore, we need to mark them volatile
so that we do not cache their contents when handling an interrupt.
This fixes a problem which can surface as occasional command timeouts.
No commands were actually timing out, but due to accessing cached data
for the CRQ in the interrupt handler, the interrupt was not processing
all command completions as it should.

Signed-off-by: Brian King <brking@linux.vnet.ibm.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>