scsi: myrs: Fix dma_alloc_coherent() error check

scsi: myrs: Fix dma_alloc_coherent() error check

[ Upstream commit edb35b1ffc686fd9b5a91902f034eb9f4d2c9f6b ]

Check for NULL return value with dma_alloc_coherent(), because DMA
address is not always set by dma_alloc_coherent() on failure.

Fixes: 77266186397c ("scsi: myrs: Add Mylex RAID controller (SCSI interface)")
Signed-off-by: Thomas Fourier <fourier.thomas@gmail.com>
Link: https://lore.kernel.org/r/20250725083112.43975-2-fourier.thomas@gmail.com
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>