[SCSI] fnic: use DMA_BIT_MASK(nn) instead of deprecated DMA_nnBIT_MASK

Robert Love reported warning while building fnic_main.c:
drivers/scsi/fnic/fnic_main.c:478: warning: `DMA_nnBIT_MASK' is deprecated.

Replaced use of DMA_nnBIT_MASK by DMA_BIT_MASK(nn)

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