tests: Avoid side effects inside g_assert() arguments

tests: Avoid side effects inside g_assert() arguments

For us, assertions are always enabled, but side-effect expressions
inside the argument to g_assert() are bad style anyway. Fix three
occurrences in IPMI related tests, which will silence some Coverity
nits.

Fixes: CID 1432322, CID 1432287, CID 1432291
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20210503165525.26221-4-peter.maydell@linaro.org>
Signed-off-by: Thomas Huth <thuth@redhat.com>