kselftests: dmabuf-heaps: Fix confused return value on expected error testing

When I added the expected error testing, I forgot I need to set
the return to zero when we successfully see an error.

Without this change we only end up testing a single heap
before the test quits.

Cc: Shuah Khan <[email protected]>
Cc: Sumit Semwal <[email protected]>
Cc: Benjamin Gaignard <[email protected]>
Cc: Brian Starkey <[email protected]>
Cc: Laura Abbott <[email protected]>
Cc: "Andrew F. Davis" <[email protected]>
Cc: [email protected]
Signed-off-by: John Stultz <[email protected]>
Signed-off-by: Shuah Khan <[email protected]>

Author: johnstultz-work

tools/testing/selftests/dmabuf-heaps/dmabuf-heap.c

@@ -351,6 +351,7 @@ static int test_alloc_errors(char *heap_name)
 	}
 
 	printf("Expected error checking passed\n");
+	ret = 0;
 out:
 	if (dmabuf_fd >= 0)
 		close(dmabuf_fd);