video: exynos-mipi-dsi: Add missing static storage class specifiers

Fixes the following sparse warnings:
drivers/video/exynos/exynos_mipi_dsi.c:208:22: warning:
symbol 'exynos_mipi_dsi_find_lcd_device' was not declared. Should it be static?
drivers/video/exynos/exynos_mipi_dsi.c:268:22: warning:
symbol 'exynos_mipi_dsi_bind_lcd_ddi' was not declared. Should it be static?

Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Acked-by: Donghwa Lee <dh09.lee@samsung.com>
Signed-off-by: Florian Tobias Schandinat <FlorianSchandinat@gmx.de>