MAINTAINERS: remove unnecessary EXYNOS DP DRIVER F: pattern

Remove unnecessary pattern for Exynos DP header from MAINTAINERS file.
After commit f9b1e013

 ("video: exynos_dp: remove non-DT support for
Exynos Display Port"), 'exynos_dp.h' has not been used.

Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>