selftests: kvm/x86: Fix the warning in lib/x86_64/processor.c

The following warning appears when executing
make -C tools/testing/selftests/kvm

include/x86_64/processor.h:290:2: warning: 'ecx' may be used uninitialized in this
function [-Wmaybe-uninitialized]
  asm volatile("cpuid"
  ^~~
lib/x86_64/processor.c:1523:21: note: 'ecx' was declared here
  uint32_t eax, ebx, ecx, edx, max_ext_leaf;

Just initialize ecx to remove this warning.

Fixes: c8cc43c1 ("selftests: KVM: avoid failures due to reserved HyperTransport region")
Signed-off-by: Jinrong Liang <cloudliang@tencent.com>
Message-Id: <20220119140325.59369-1-cloudliang@tencent.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

tools/testing/selftests/kvm/lib/x86_64/processor.c

@@ -1535,6 +1535,7 @@ unsigned long vm_compute_max_gfn(struct kvm_vm *vm)
 	/* Before family 17h, the HyperTransport area is just below 1T.  */
 	ht_gfn = (1 << 28) - num_ht_pages;
 	eax = 1;
+	ecx = 0;
 	cpuid(&eax, &ebx, &ecx, &edx);
 	if (x86_family(eax) < 0x17)
 		goto done;