staging: greybus: loopback_test: Remove void function return statement

Void function return statement is not useful in this case. Issue
reported by checkpatch.
Reviewed-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Jack Schofield <schofija@oregonstate.edu>
Link: https://lore.kernel.org/r/5d465d56a6e3de2cb9d2f34377cbb82678cc67b1.1669872193.git.schofija@oregonstate.eduSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/greybus/tools/loopback_test.c

@@ -862,7 +862,6 @@ void loopback_run(struct loopback_test *t)
 
 err:
 	printf("Error running test\n");
-	return;
 }
 
 static int sanity_check(struct loopback_test *t)