hp_wireless: Inform the user if hp_wireless_input_setup()/add() fails

In hpwl_add() there is a unused variable err to which we assign the
result of hp_wireless_input_setup() but we don't do anything depending
on the result so print out a message that informs the user if add()
(hp_wireless_input_setup()) fails since acpi_device_probe() doesn't
print anything in this case.

Signed-off-by: Giedrius Statkevicius <giedriuswork@gmail.com>
Signed-off-by: Darren Hart <dvhart@linux.intel.com>