drm: bridge: samsung-dsim: Initialize ULPS EXIT for i.MX8M DSIM

The ULPS EXIT is initialized to 0xaf in downstream BSP as well as older
revisions of this patchset, in newer revisions of the DSIM patchset it
was left out and set to 0. Fix it.

Fixes: 4d562c70 ("drm: bridge: samsung-dsim: Add i.MX8M Mini/Nano support")
Signed-off-by: Marek Vasut <marex@denx.de>
Reviewed-by: Robert Foss <rfoss@kernel.org>
Signed-off-by: Robert Foss <rfoss@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230709134827.449185-1-marex@denx.de