video: exynos_dp: replace char pointer with char array for adjust_request variable

The char pointer for adjust_request variable is replaced with char array
to fix possible null pointer dereference when clock recovery is failed.

Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Signed-off-by: Florian Tobias Schandinat <FlorianSchandinat@gmx.de>