drm/bridge: display-connector: fix an uninitialized pointer in probe()

The "label" pointer is used for debug output.  The code assumes that it
is either NULL or valid, but it is never set to NULL.  It is either
valid or uninitialized.

Fixes: 0c275c30 ("drm/bridge: Add bridge driver for display connectors")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20211013080825.GE6010@kili