spi: orion: fix potential NULL pointer de-reference

It's possible that the call to of_match_device() (introduced in commit
df59fa7f ["spi: orion: support armada extended baud rates"]) may return
a NULL if there is no match in the device tree (or perhaps no device tree
at all). Check the return pointer and set the local device data to the
lowest common denominator orion device data if it is NULL.

Reported-by: Karl Beldan <karl.beldan@gmail.com>
Signed-off-by: Greg Ungerer <gerg@uclinux.org>
Signed-off-by: Mark Brown <broonie@kernel.org>