main: Some logging cleanups
main: Some logging cleanups

* replaced g_error with g_warning as g_error means 'unexpected critical
  programming error' and triggered a core dump

Signed-off-by: Enrico Jorns <a2e5f936c390f36494e46e71bcfbe365bb1e8c49@pengutronix.de>

rauc/rauc,ejoerns/rauc,ejoerns/rauc,rauc/rauc,jluebbe/rauc,jluebbe/rauc,rauc/rauc,ejoerns/rauc,jluebbe/rauc