spi: ti-qspi: Fixup driver name

The driver name in current code looks like a compatible string which is not
the naming convention for platform drivers.
Fix it and also add modalias since this driver can be built as a module.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Acked-by: Sourav Poddar <sourav.poddar@ti.com>
Signed-off-by: Mark Brown <broonie@linaro.org>