scsi: aic7xxx: remove set but not used variable 'shared_scb_data'

Fixes gcc '-Wunused-but-set-variable' warning:

drivers/scsi/aic7xxx/aic79xx_pci.c: In function 'ahd_pci_config':
drivers/scsi/aic7xxx/aic79xx_pci.c:291:19: warning:
 variable 'shared_scb_data' set but not used [-Wunused-but-set-variable]

Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>