greybus: gb-audio: Set clock edges to match rt5647 codec requirements

The rt5647 codec on speaker and mediabar modules require that
the following clock edge settings:

	ll_wclk_change_edge	GB_I2S_MGMT_EDGE_FALLING
	ll_wclk_tx_edge		GB_I2S_MGMT_EDGE_RISING
	ll_wclk_rx_edge		GB_I2S_MGMT_EDGE_FALLING

(Those are the setting that work, at least).  So make the Greybus
audio driver configure the GPBridge with those settings.

Signed-off-by: Mark A. Greer <mgreer@animalcreek.com>
Tested-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>