Out of the three callers once insists on the scratch buffer, and the
others are fine with a new allocation.  Switch those two to just use
pci_alloc_consistent directly, and open code the scratch buffer
allocation in the remaining one.  This avoids a case where we might
be doing a memory allocation under a spinlock with irqs disabled.

[mkp: typo]
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>