device.h: fix bad error message for Z_DEVICE_NAME_CHECK

The error message for Z_DEVICE_NAME_CHECK was needlessly calling
DEVICE_NAME_GET() on the "name" string, resulting in a confusing message
being displayed.

Remove the DEVICE_NAME_GET call so that the error message shown by the
compiler contains the actual name.

Signed-off-by: Luca Burelli <l.burelli@arduino.cc>