[SCSI] zfcp: Simplify mask lookups for incoming RSCNs

Use an array for looking up the mask corresponding to the 2-bit
information instead of the switch/case.

Signed-off-by: Christof Schmitt <christof.schmitt@de.ibm.com>
Acked-by: Felix Beck <felix@linux.vnet.ibm.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>