slimbus: core: fix of_slim_get_device() kernel doc

slimbus: core: fix of_slim_get_device() kernel doc

Unlike slim_get_device() the of_slim_get_device() helper does not
allocate and register any slimbus devices in case lookup fails.

Update the of_slim_get_device() kernel doc to reflect this and add a
comment about the helper taking a reference to the returned device.

Fixes: e0772de8a48b ("slimbus: core: add of_slim_device_get() helper")
Signed-off-by: Johan Hovold <johan@kernel.org>
Link: https://patch.msgid.link/20251126145329.5022-6-johan@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>