scsi: mac_esp: Avoid type warning from sparse

Avoid the following warning from "make C=1":

  CHECK   drivers/scsi/mac_esp.c
drivers/scsi/mac_esp.c:357:30: warning: incorrect type in initializer (different address spaces)
drivers/scsi/mac_esp.c:357:30:    expected unsigned char [usertype] *fifo
drivers/scsi/mac_esp.c:357:30:    got void [noderef] <asn:2>*

Tested-by: Stan Johnson <userm57@yahoo.com>
Signed-off-by: Finn Thain <fthain@telegraphics.com.au>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>