flexcan: Prefer device tree clock frequency if available.

flexcan: Prefer device tree clock frequency if available.

If our CAN device's device tree node has a clock-frequency property,
then use that value for the can devices clock frequency.  If not, fall
back to asking the platform/mach code for the clock frequency associated
with the flexcan device.

Signed-off-by: Robin Holt <[email protected]>
Acked-by: Wolfgang Grandegger <[email protected]>,
Cc: Kumar Gala <[email protected]>
Cc: Marc Kleine-Budde <[email protected]>,
Cc: U Bhaskar-B22300 <[email protected]>
Cc: Scott Wood <[email protected]>
Cc: Grant Likely <[email protected]>
Cc: [email protected],
Cc: [email protected],
Cc: PPC list <[email protected]>
Cc: [email protected]
Signed-off-by: David S. Miller <[email protected]>