drm/omap: Fix possible NULL dereference

drm/omap: Fix possible NULL dereference

smatch reports:

drivers/gpu/drm/omapdrm/dss/base.c:176 omapdss_device_disconnect() error: we previously assumed 'src' could be null (see line 169)

This code is mostly from a time when omapdrm had its own display device
model. I can't honestly remember the details, and I don't think it's
worth digging in deeply into that for a legacy driver.

However, it looks like we only call omapdss_device_disconnect() and
omapdss_device_connect() with NULL as the src parameter. We can thus
drop the src parameter from both functions, and fix the smatch warning.

I don't think omapdss_device_disconnect() ever gets NULL for the dst
parameter (if it did, we'd crash soon after returning from the
function), but I have kept the !dst check, just in case, but I added a
WARN_ON() there.

Also, if the dst parameter can be NULL, we can't always get the struct
dss_device pointer from dst->dss (which is only used for a debug print).
To make sure we can't hit that issue, do it similarly to the
omapdss_device_connect() function: add 'struct dss_device *dss' as the
first parameter, so that we always have it regardless of the dst.

Fixes: 79107f274b2f ("drm/omap: Add support for drm_bridge")
Reviewed-by: Sebastian Reichel <sebastian.reichel@collabora.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240806-omapdrm-misc-fixes-v1-1-15d31aea0831@ideasonboard.com