powerpc/85xx: Fix up clock_freq property in CAN node of dts

Fix up the device tree property associated with the Flexcan clock
frequency. This property is used to calculate the bit timing parameters
for Flexcan.

Signed-off-by: Bhaskar Upadhaya <Bhaskar.Upadhaya@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>