xen/PVonHVM: fix compile warning in init_hvm_pv_info

After merging the xen-two tree, today's linux-next build (x86_64
allmodconfig) produced this warning:

arch/x86/xen/enlighten.c: In function 'init_hvm_pv_info':
arch/x86/xen/enlighten.c:1617:16: warning: unused variable 'ebx' [-Wunused-variable]
arch/x86/xen/enlighten.c:1617:11: warning: unused variable 'eax' [-Wunused-variable]

Introduced by commit 9d02b43d ("xen PVonHVM: use E820_Reserved area
for shared_info").
Signed-off-by: NOlaf Hering <olaf@aepfle.de>
Signed-off-by: NKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>

arch/x86/xen/enlighten.c

@@ -1578,7 +1578,7 @@ static void __init xen_hvm_init_shared_info(void)
 
 static void __init init_hvm_pv_info(void)
 {
-	uint32_t eax, ebx, ecx, edx, pages, msr, base;
+	uint32_t ecx, edx, pages, msr, base;
 	u64 pfn;
 
 	base = xen_cpuid_base();