drm/managed: Simplify if condition

The if condition !A || A && B can be simplified to !A || B.

Fixes the following Coccinelle/coccicheck warning reported by
excluded_middle.cocci:

	WARNING !A || A && B is equivalent to !A || B

Compile-tested only.

Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: Thorsten Blum <thorsten.blum@toblux.com>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20240701195607.228852-1-thorsten.blum@toblux.com