x86/Viridian: fix error code use

x86/Viridian: fix error code use

Both the wrong use of HV_STATUS_* and the return type of
hv_vpset_to_vpmask() can lead to viridian_hypercall()'s
ASSERT_UNREACHABLE() triggering when translating error codes from Xen
to Viridian representation.

Fixes: b4124682db6e ("viridian: add ExProcessorMasks variants of the flush hypercalls")
Fixes: 9afa867d42ba ("viridian: add ExProcessorMasks variant of the IPI hypercall")
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Paul Durrant <paul@xen.org>