ARM: dts: Fix typo for omap4 mcasp rx path

As reported by Peter Ujfalusi <peter.ujfalusi@ti.com>, the rx path on macsp
is disabled and only tx is usable if the davinci-mcasp driver is updated for
it.

Reported-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>