video: exynos_mipi_dsi: Unlock the mutex before returning

Mutex should be unlocked before returning. Fixes mutex lock-unlock
imbalance issue.

Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>

diff --cc drivers/video/exynos/exynos_mipi_dsi_common.c
Simple merge