Correcting the discovery method for SPI port. The current method is based
upon knowledge of a specific port and a *_DRV_NAME value. Instead this
should be based upon the use of the device_get_binding() for SPI_0.
Change-Id: I250f5dddf2a2e79c4714addf647b0c74bd79ec5a
Signed-off-by: Dan Kalowsky <daniel.kalowsky@intel.com>