fix always succesful memory test

Since 51209b1f ("Use common mtest iteration counting"),
do_mem_mtest has always reported 0 errors and hence returned 0, even
if errors were detected. Fix the helpers mem_test_alt() and
mem_test_quick() to return the number of errors found.
Signed-off-by: NRasmus Villemoes <rasmus.villemoes@prevas.dk>

common/cmd_mem.c

@@ -931,7 +931,7 @@ static ulong mem_test_alt(vu_long *buf, ulong start_addr, ulong end_addr,
 		addr[offset] = 0;
 	}
 
-	return 0;
+	return errs;
 }
 
 static ulong mem_test_quick(vu_long *buf, ulong start_addr, ulong end_addr,
@@ -990,7 +990,7 @@ static ulong mem_test_quick(vu_long *buf, ulong start_addr, ulong end_addr,
 		val += incr;
 	}
 
-	return 0;
+	return errs;
 }
 
 /*