drm/tilcdc: remove broken error handling

Remove broken error handling. The condition for handling the
LCDC_SYNC_LOST and LCDC_FIFO_UNDERFLOW could never be satisfied as the
LCDC_SYNC_LOST interrupt is not enabled. Also the requirement to have
both LCDC_SYNC_LOST and LCDC_FIFO_UNDERFLOW fired at once before
handling the error looks weird.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
[Added description to the patch]
Signed-off-by: Jyri Sarha <jsarha@ti.com>