tests/qtest/m48t59-test: Silence compiler warning with -Wshadow

tests/qtest/m48t59-test: Silence compiler warning with -Wshadow

When compiling this file with -Wshadow=local , we get:

../tests/qtest/m48t59-test.c: In function ‘bcd_check_time’:
../tests/qtest/m48t59-test.c:195:17: warning: declaration of ‘s’
 shadows a previous local [-Wshadow=local]
  195 |         long t, s;
      |                 ^
../tests/qtest/m48t59-test.c:158:17: note: shadowed declaration is here
  158 |     QTestState *s = m48t59_qtest_start();
      |                 ^

Rename the QTestState variable to "qts" which is the common
naming for such a variable in other tests.

Reported-by: Markus Armbruster <armbru@redhat.com>
Message-ID: <20230922163742.149444-1-thuth@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: "Daniel P. Berrangé" <berrange@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>