selftests/proc: fix array_size.cocci warning

Fix the following coccicheck warning:

tools/testing/selftests/proc/proc-pid-vm.c:371:26-27:
WARNING: Use ARRAY_SIZE
tools/testing/selftests/proc/proc-pid-vm.c:420:26-27:
WARNING: Use ARRAY_SIZE

It has been tested with gcc (Debian 8.3.0-6) 8.3.0 on x86_64.
Signed-off-by: Guo Zhengkui <guozhengkui@vivo.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

tools/testing/selftests/proc/proc-pid-vm.c

@@ -46,6 +46,8 @@
 #include <sys/time.h>
 #include <sys/resource.h>
 
+#include "../kselftest.h"
+
 static inline long sys_execveat(int dirfd, const char *pathname, char **argv, char **envp, int flags)
 {
 	return syscall(SYS_execveat, dirfd, pathname, argv, envp, flags);
@@ -368,7 +370,7 @@ int main(void)
 		};
 		int i;
 
-		for (i = 0; i < sizeof(S)/sizeof(S[0]); i++) {
+		for (i = 0; i < ARRAY_SIZE(S); i++) {
 			assert(memmem(buf, rv, S[i], strlen(S[i])));
 		}
 
@@ -417,7 +419,7 @@ int main(void)
 		};
 		int i;
 
-		for (i = 0; i < sizeof(S)/sizeof(S[0]); i++) {
+		for (i = 0; i < ARRAY_SIZE(S); i++) {
 			assert(memmem(buf, rv, S[i], strlen(S[i])));
 		}
 	}