scsi: aic7xxx: remove unused redundant variable num_chip_names

Variable num_chip_names is defined but not used, hence it is redundant and can
be removed.

Cleans up clang warning:
'num_chip_names' defined but not used [-Wunused-const-variable=]

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>