drm/bridge: tc358767: fix initial DP0/1_SRCCTRL value

Initially DP0_SRCCTRL is set to a static value which includes
DP0_SRCCTRL_LANES_2 and DP0_SRCCTRL_BW27, even when only 1 lane of
1.62Gbps speed is used. DP1_SRCCTRL is configured to a magic number.

This patch changes the configuration as follows:

Configure DP0_SRCCTRL by using tc_srcctrl() which provides the correct
value.

DP1_SRCCTRL needs two bits to be set to the same value as DP0_SRCCTRL:
SSCG and BW27. All other bits can be zero.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Reviewed-by: Andrzej Hajda <a.hajda@samsung.com>
Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190103115954.12785-5-tomi.valkeinen@ti.com