[SCSI] aacraid: prevent panic on adapter resource failure

If the driver fails to allocate the contiguous (DMAable) memory for
system reasons, we fail to load the instance, but then we try to free
the <nul> allocation in the cleanup code and we get a panic in
pci_free_consistent(). This is reported against an older kernel, hope
this is relevant for latest/greatest.

Signed-off-by: Mark Salyzyn <aacraid@adaptec.com>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>