Looks as though 'ahc' hasn't been used since 2005.

Fixes the following W=1 kernel build warning(s):

 drivers/scsi/aic7xxx/aic7xxx_osm.c: In function ‘ahc_linux_slave_configure’:
 drivers/scsi/aic7xxx/aic7xxx_osm.c:674:20: warning: variable ‘ahc’ set but not used [-Wunused-but-set-variable]
 674 | struct ahc_softc *ahc;
 | ^~~

Link: https://lore.kernel.org/r/20200713074645.126138-20-lee.jones@linaro.org
Cc: Hannes Reinecke <hare@suse.com>
Cc: "Daniel M. Eischen" <deischen@iworks.InterWorks.org>
Cc: Doug Ledford <dledford@redhat.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>