cpu: vmexit: Handle KVM_EXIT_MEMORY_FAULT correctly

Linux kernel documentation states:

"Note! KVM_EXIT_MEMORY_FAULT is unique among all KVM exit reasons in
that it accompanies a return code of '-1', not '0'! errno will always be
set to EFAULT or EHWPOISON when KVM exits with KVM_EXIT_MEMORY_FAULT,
userspace should assume kvm_run.exit_reason is stale/undefined for all
other error numbers." "

Update the KVM_RUN ioctl error handling to correctly handle
KVM_EXIT_MEMORY_FAULT.

Signed-off-by: Aneesh Kumar K.V (Arm) <aneesh.kumar@kernel.org>