spi/sirf: fix MODULE_DEVICE_TABLE

This fixes building the spi-sirf driver as a loadable module, which uses
an incorrect MODULE_DEVICE_TABLE, by changing the reference to the
correct symbol.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>