x86: Convert vmx_tests.c comments to ASCII

Some strange characters snuck into this file. Convert them to ASCII
for better readability.

Signed-off-by: Jim Mattson <jmattson@google.com>
Message-Id: <20210511220949.1019978-1-jmattson@google.com>
Reviewed-by: David Matlack <dmatlack@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>