xen: xen_init_cpuid_mask: Zero cx before calling xen_cpuid

CPUID function 1 doesn't use cx, but xen_cpuid doesn't know that, resulting in this warning:

arch/x86/xen/enlighten.c: In function ‘xen_start_kernel’:
arch/x86/xen/enlighten.c:192: warning: ‘cx’ may be used uninitialized in this function arch/x86/xen/enlighten.c:205: note: ‘cx’ was declared here

Set cx = 0 to avoid this warning. This seems preferable to implementing a xen_cpuid_nocount without the input constraint for cx, and either of those seem preferable to just ignoring the warning.

---

Build-tested only.

 arch/x86/xen/enlighten.c |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)

index 0a1700a..6ee2ef8 100644
@@ -215,6 +215,7 @@ static __init void xen_init_cpuid_mask(void)
 			  (1 << X86_FEATURE_ACPI));  /* disable ACPI */
 
 	ax = 1;
+	cx = 0;
 	xen_cpuid(&ax, &bx, &cx, &dx);
 
 	/* cpuid claims we support xsave; try enabling it to see what happens */

1.5.6.5

Thanks, applied.

J