tests: Fix hello.c test program

Update the hello test to have a sane return code.

Change-Id: I9576b71ee995d8aa410c4ed19d44cc4e9fad10ee
Signed-off-by: Jason Lowe-Power <jason@lowepower.com>
Reviewed-on: https://gem5-review.googlesource.com/4881
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Reviewed-by: Anthony Gutierrez <anthony.gutierrez@amd.com>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Anthony Gutierrez <anthony.gutierrez@amd.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>

tests/test-progs/hello/src/hello.c

@@ -30,8 +30,9 @@
 
 #include <stdio.h>
 
-int main()
+int main(int argc, char* argv[])
 {
     printf("Hello world!\n");
+    return 0;
 }