powerpc/fsl-cpm: Configure clock correctly for SCC

Some board setup functions call cpm1_clk_setup() or cmp2_clk_setup()
to configure the clock source.

If CPM_CLK_RTX has been used for the parameter mode,
the clock has been configured only for TX but not for RX.

With this patch CPM_CLK_RTX configures the clock for both directions
correctly.

Signed-off-by: Wolfgang Ocker <weo@reccoware.de>
Acked-by: Scott Wood <scottwood@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>