tests/qtest/npcm7xx_pwm-test.c: Avoid g_assert_true() for non-test assertions

tests/qtest/npcm7xx_pwm-test.c: Avoid g_assert_true() for non-test assertions

In the glib API, the distinction between g_assert() and
g_assert_true() is that the former is for "bug, terminate the
application" and the latter is for "test check, on failure either
terminate or just mark the testcase as failed".  For QEMU, g_assert()
is always fatal, so code can assume that if the assertion fails
execution does not proceed, but this is not true of g_assert_true().

In npcm7xx_pwm-test, the pwm_index() and pwm_module_index() functions
include some assertions that are just guarding against possible bugs
in the test code that might lead us to out-of-bounds array accesses.
These should use g_assert() because they aren't part of what the test
is testing and the code does not correctly handle the case where the
condition was false.

This fixes some Coverity issues where Coverity knows that
g_assert_true() can continue when the condition is false and
complains about the possible array overrun at various callsites.

Fixes: Coverity CID 1442340, 1442341, 1442343, 1442344, 1442345, 1442346
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Hao Wu <wuhaotsh@google.com>
Reviewed-by: Havard Skinnemoen <hskinnemoen@google.com>
Message-Id: <20210505135516.21097-1-peter.maydell@linaro.org>
Signed-off-by: Thomas Huth <thuth@redhat.com>