nvme-pci: propagate (some) errors from host memory buffer setup

We want to catch command execution errors when resetting the device, so
propagate errors from the Set Features when setting up the host memory
buffer.  We keep ignoring memory allocation failures, as the spec
clearly says that the controller must work without a host memory buffer.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Keith Busch <keith.busch@intel.com>
Cc: stable@vger.kernel.org