drm/exynos: Remove redundant check in exynos_drm_fimd.c file

devm_request_and_ioremap function checks the validity of the
pointer returned by platform_get_resource. Hence an additional check
in the probe function is not necessary.

Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Signed-off-by: Inki Dae <inki.dae@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>