spi: spi-altera: Use of_match_ptr

Instead of having to define the match table to NULL if CONFIG_OF isn't
set, use the of_match_ptr() macro which will do this for us.

Signed-off-by: Tobias Klauser <tklauser@distanz.ch>
Acked-by: Rob Herring <rob.herring@calxeda.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>