spi: efm32: Fix build error

Obviously the of_device_id table name is wrong.

Fix below build error:

  CC [M]  drivers/spi/spi-efm32.o
drivers/spi/spi-efm32.c:499:1: error: '__mod_of_device_table' aliased to undefined symbol 'efm32_uart_dt_ids'
make[2]: *** [drivers/spi/spi-efm32.o] Error 1
make[1]: *** [drivers/spi] Error 2
make: *** [drivers] Error 2

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Signed-off-by: Mark Brown <broonie@linaro.org>