test: fix naming of test functions in the log test suite

Both the nolog as well as the syslog tests were not found by Python
function generate_ut_subtest() due to not following the nameing
requirements imposed by the regular expression used to find linker
generated list entries in file u-boot.sym.

Adjust the naming of test functions.

With the patch the following tests are executed successfully for
sandbox_defconfig:

test/py/tests/test_ut.py::test_ut[ut_log_syslog_debug] PASSED
test/py/tests/test_ut.py::test_ut[ut_log_syslog_err] PASSED
test/py/tests/test_ut.py::test_ut[ut_log_syslog_info] PASSED
test/py/tests/test_ut.py::test_ut[ut_log_syslog_nodebug] PASSED
test/py/tests/test_ut.py::test_ut[ut_log_syslog_notice] PASSED
test/py/tests/test_ut.py::test_ut[ut_log_syslog_warning] PASSED

The nolog tests are only executed if CONFIG_LOG=n and
CONFIG_CONSOLE_RECORD=y.

Reported-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>