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

This reverts commit eb9635b4 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: Ifeda5fca1bf9a45e7264ab123d0a69210bb506cc
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>