altera_spi: add spi_set_speed

Added this for mmc_spi driver. Though altera spi core does not
support programmable speed. It is fixed when configured in
sopc-builder.

Signed-off-by: Thomas Chou <thomas@wytron.com.tw>
Signed-off-by: Scott McNutt <smcnutt@psyent.com>
1 file changed