PCI: hv: Take a const cpumask in hv_compose_msi_req_get_cpu()

The cpumask that is passed to this function ultimately comes from
irq_data_get_effective_affinity_mask(), which was recently changed to
return a const cpumask pointer. The first level of functions handling
the affinity mask were updated, but not this helper function.

Fixes: 4d0b8298 ("genirq: Return a const cpumask from irq_data_get_affinity_mask")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Samuel Holland <samuel@sholland.org>
Reviewed-by: Michael Kelley <mikelley@microsoft.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20220708004931.1672-1-samuel@sholland.org