x86/domctl: don't ignore errors from vmce_restore_vcpu()
What started out as a simple cleanup patch (eliminating the redundant
check of domctl->cmd before setting "copyback", which as a result
turned the "ext_vcpucontext_out" label useless) revealed a bug in the
handling of XEN_DOMCTL_set_ext_vcpucontext.
Fix this, retaining the cleanup, and at once dropping a stale comment
and an accompanying formatting issue.
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>