Revert "drm/mipi-dsi: use correct return type for the DSC functions"

This reverts commit 26f73934 which is
commit de1c705c upstream.

It breaks the Android kernel abi and can be brought back in the future
in an abi-safe way if it is really needed.

Bug: 161946584
Change-Id: Ib7f794ccd2b16db0b8958640ad7bd8f4e5c7296a
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>