selftests/powerpc: Use "Delta" rather than "Error" in normal output

Use "Delta" to refer to the difference between measurements, rather than
"Error", so scripts that look for "Error" aren't confused into thinking
there was a failure.
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

tools/testing/selftests/powerpc/pmu/ebb/instruction_count_test.c

@@ -51,7 +51,7 @@ static int do_count_loop(struct event *event, uint64_t instructions,
 		printf("Looped for %lu instructions, overhead %lu\n", instructions, overhead);
 		printf("Expected %lu\n", expected);
 		printf("Actual   %llu\n", event->result.value);
-		printf("Error    %ld, %f%%\n", difference, percentage);
+		printf("Delta    %ld, %f%%\n", difference, percentage);
 		printf("Took %d EBBs\n", ebb_state.stats.ebb_count);
 	}