drm/exynos: remove superfluous error messages

The messages are redundant since 'check_fb_gem_memory_type'
already prints out exactly the same string when it fails.

Reviewed-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
Signed-off-by: Tobias Jakobi <tjakobi@math.uni-bielefeld.de>
Acked-by: Joonyoung Shim <jy0922.shim@samsung.com>
Signed-off-by: Inki Dae <inki.dae@samsung.com>