USB: usbatm: move the atm_dbg() call to use dynamic debug

Move the atm_dbg() call to use the dynamic debug subsystem, and not rely
on CONFIG_USB_DEBUG for if things should be printed out or not.

This also means the drivers do not have to be rebuilt to get debugging
messages, important for getting information from users who can not
rebuild their kernels.

Acked-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>