logging_test: fix compile warning from oe-sdk
logging_test: fix compile warning from oe-sdk

Update the variable holding the return from getopt_long to
be int, matching the manpage expectation, to resolve the
following compile warning:

    ../logging_test.cpp:244:47: error: comparison is always true due
    to limited range of data type [-Werror=type-limits]
  243 |     while ((arg = getopt_long(argc, argv, "hc:", long_options,
      |            ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  244 |                               &option_index)) != -1)
      |                               ~~~~~~~~~~~~~~~~^~~~~

Signed-off-by: Patrick Williams <cbb7353e6d953ef360baf960c122346276c6e320@stwcx.xyz>
Change-Id: I3985c96081a116a628c47c4e0329dad70af3e766

openbmc/phosphor-logging,openbmc/phosphor-logging,openbmc/phosphor-logging,openbmc/phosphor-logging