Use a default clock speed of 48Mhz, instead of ending up with 0,
if platforms fail to specify a valid clock speed.
Signed-off-by: NRajendra Nayak <rnayak@ti.com>
Reviewed-by: NRob Herring <rob.herring@calxeda.com>
Signed-off-by: NTony Lindgren <tony@atomide.com>