PCI: hv: Allocate interrupt descriptors with GFP_ATOMIC

The memory allocation here needs to be non-blocking.  Fix the issue.

Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Long Li <longli@microsoft.com>
Cc: <stable@vger.kernel.org>