drm/exynos: remove fimd_mode_fixup()

The only thing mode_fixup was doing was set the adjusted_mode->vrefresh to
60, but it already has the value of 60 when the fimd_mode_fixup() is
called. That means this call is actually pointless and can be removed.

Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
Signed-off-by: Inki Dae <inki.dae@samsung.com>