drm/komeda: Fix typos in komeda_splitter_validate

Fix both the string and the struct member being printed.

Changes since v1:
 - Now with a bonus grammar fix, too.

Fixes: 264b9436

 ("drm/komeda: Enable writeback split support")
Reviewed-by: James Qian Wang (Arm Technology China) <james.qian.wang@arm.com>
Signed-off-by: Mihail Atanassov <mihail.atanassov@arm.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190930122231.33029-1-mihail.atanassov@arm.com