driver core: Change delimiter in devlink device's name to "--"

The devlink device name is of the form "supplier:consumer". But ":" is
fairly common in device names and makes it visually hard to distinguish
supplier and consumer. So, replace it with "--" to make it easier.

Signed-off-by: Saravana Kannan <saravanak@google.com>
Link: https://lore.kernel.org/r/20200724180523.1393383-1-saravanak@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>