drm/exynos/fimd: don't initialize 'ret' variable in fimd_probe()

We  set it in the beginning of the function, thus no need to set it at
initialization.

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