Why is the argument to ->mode_valid() called "crtc"?
I guess a copy/paste error. Fix it.

Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20180129095531.4557-1-linus.walleij@linaro.org