fix(test): check for mmap errors before using pointer

mmap should never fail, but having the check for failure after the
memset is just wrong.

Signed-off-by: Patrick Roy <[email protected]>

Author: roypat

resources/overlay/usr/local/bin/fast_page_fault_helper.c

@@ -30,13 +30,13 @@ int main(int argc, char *const argv[]) {
 
     ptr = mmap(NULL, MEM_SIZE_MIB, PROT_READ | PROT_WRITE, MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
 
-    memset(ptr, 1, MEM_SIZE_MIB);
-
     if (MAP_FAILED == ptr) {
         perror("mmap");
         return -1;
     }
 
+    memset(ptr, 1, MEM_SIZE_MIB);
+
     sigwait(&set, &signal);
 
     memset(ptr, 2, MEM_SIZE_MIB);