tests/qtest/rtc-test: Remove pointless NULL check

tests/qtest/rtc-test: Remove pointless NULL check

In rtc-test.c we know that s is non-NULL because qtest_start()
will return a non-NULL value, and we assume this when we
pass s to qtest_irq_intercept_in(). So we can drop the
initial assignment of NULL and the "if (s)" condition at
the end of the function.

Fixes: Coverity CID 1432353
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20210503165525.26221-3-peter.maydell@linaro.org>
Signed-off-by: Thomas Huth <thuth@redhat.com>