tools: testing: selftests: mq_perf_tests: Fix infinite loop on ARM

We can't use a char type to check for a negative return value since char
isn't guaranteed to be signed. Indeed, the char type tends to be unsigned on
ARM.

Signed-off-by: dann frazier <[e-mail]>
Signed-off-by: Shuah Khan <[e-mail]>

tools/testing/selftests/mqueue/mq_perf_tests.c

···
 {
 	struct mq_attr attr;
 	char *option, *next_option;
-	int i, cpu;
+	int i, cpu, rc;
 	struct sigaction sa;
 	poptContext popt_context;
-	char rc;
 	void *retval;
 
 	main_thread = pthread_self();