drivers/video/exynos/exynos_mipi_dsi.c: use devm_* APIs

devm_* APIs are device managed and make exit and cleanup code simpler.
While at it also remove some unused labels and fix an error path.

Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Acked-by: Donghwa Lee <dh09.lee@samsung.com>
Cc: Inki Dae <inki.dae@samsung.com>
Cc: Florian Tobias Schandinat <FlorianSchandinat@gmx.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>