drm/exynos: fimd: remove unused variable

The patch removes unused vidcon0 field from fimd_context structure.

Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
Reviewed-by: Tomasz Figa <t.figa@samsung.com>
Signed-off-by: Inki Dae <inki.dae@samsung.com>