Define a literal '0' asm input constraint to aarch64/page_fault_test's
guest_cas() as an unsigned long to make clang happy.

  tools/testing/selftests/kvm/aarch64/page_fault_test.c:120:16: error:
    value size does not match register size specified by the constraint
    and modifier [-Werror,-Wasm-operand-widths]
                       :: "r" (0), "r" (TEST_DATA), "r" (guest_test_memory));
                               ^
  tools/testing/selftests/kvm/aarch64/page_fault_test.c:119:15: note:
    use constraint modifier "w"
                       "casal %0, %1, [%2]\n"
                              ^~
                              %w0

Fixes: 35c58101 ("KVM: selftests: aarch64: Add aarch64/page_fault_test")
Cc: Ricardo Koller <ricarkol@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-Id: <20221213001653.3852042-2-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>