drm/amd/display: Add reset for SYMCLKC_FE_SRC_SEL

To prevent confusion after symclk has already been disabled.

Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Reviewed-by: Meenakshikumar Somasundaram <meenakshikumar.somasundaram@amd.com>
Acked-by: Qingqing Zhuo <qingqing.zhuo@amd.com>
Signed-off-by: Taimur Hassan <syed.hassan@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>