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.edu


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>