[SCSI] qla2xxx: handle default case in qla2x00_request_firmware()

This silences a static checker warning.  Also we're always adding new
types of firmware, so it might fix a bug in real life some day.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Chad Dupuis <chad.dupuis@qlogic.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>