scsi: aic7xxx: make a couple of functions static

Functions ahc_devlimited_syncrate and ahc_linux_initialize_scsi_bus are
declared static in their prototypes but are missing in their
definitions, so add the missing static.

Cleans up sparse warnings: symbol 'ahc_devlimited_syncrate' was not
declared. Should it be static?  symbol 'ahc_linux_initialize_scsi_bus'
was not declared. Should it be static?

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>