drm/amd/display: fix spelling mistake "exeuction" -> "execution"

There are spelling mistakes in a DC_ERROR message and a comment.
Fix these.

Reviewed-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>