KVM: arm64: selftests: Disable single-step with correct KVM define

Disable single-step by setting debug.control to KVM_GUESTDBG_ENABLE,
not to SINGLE_STEP_DISABLE.  The latter is an arbitrary test enum that
just happens to have the same value as KVM_GUESTDBG_ENABLE, and so
effectively disables single-step debug.

No functional change intended.

Cc: Reiji Watanabe <reijiw@google.com>
Fixes: b18e4d4 ("KVM: arm64: selftests: Add a test case for KVM_GUESTDBG_SINGLESTEP")
Signed-off-by: Sean Christopherson <seanjc@google.com>
Link: https://lore.kernel.org/r/20221117002350.2178351-2-seanjc@google.com
Reviewed-by: Oliver Upton <oliver.upton@linux.dev>

tools/testing/selftests/kvm/aarch64/debug-exceptions.c

@@ -369,7 +369,7 @@ void test_single_step_from_userspace(int test_cnt)
 						KVM_GUESTDBG_SINGLESTEP;
 				ss_enable = true;
 			} else {
-				debug.control = SINGLE_STEP_DISABLE;
+				debug.control = KVM_GUESTDBG_ENABLE;
 				ss_enable = false;
 			}