scsi: ultrastor.c depends on ISA_DMA_API

Fix build when CONFIG_ISA_DMA_API is not enabled. Fixes these build
errors (on x86_64):

../drivers/scsi/ultrastor.c: In function 'ultrastor_14f_detect':
../drivers/scsi/ultrastor.c:519:5: error: implicit declaration of function 'request_dma' [-Werror=implicit-function-declaration]
     if (config.dma_channel && request_dma(config.dma_channel,"Ultrastor")) {
     ^
../drivers/scsi/ultrastor.c: In function 'ultrastor_release':
../drivers/scsi/ultrastor.c:658:3: error: implicit declaration of function 'free_dma' [-Werror=implicit-function-declaration]
   free_dma(shost->dma_channel);
   ^

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>