KVM: arm64: Refactor setting the return value in kvm_vm_ioctl_enable_cap()

Initialize r = -EINVAL to get rid of the error-path
initializations in kvm_vm_ioctl_enable_cap().

No functional change intended.

Suggested-by: Oliver Upton <oliver.upton@linux.dev>
Signed-off-by: Fuad Tabba <tabba@google.com>
Acked-by: Oliver Upton <oliver.upton@linux.dev>
Link: https://lore.kernel.org/r/20240423150538.2103045-29-tabba@google.com


Signed-off-by: Marc Zyngier <maz@kernel.org>