usb: gadget: function: Simplify diagnostic messaging in printer

Don't issue messages which can be easily achieved with ftrace.
In case of printer_open() the return code is propagated to other layers
so the user will know about -EBUSY anyway.

Signed-off-by: Andrzej Pietrasiewicz <andrzej.p@collabora.com>
Link: https://lore.kernel.org/r/20221123110746.59611-1-andrzej.p@collabora.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>