USB: usblcd.c: remove dbg() usage

dbg() was a very old USB-specific macro that should no longer
be used. This patch removes it from being used in the driver
and uses dev_dbg() instead.

CC: Zack Parsons <k3bacon@gmail.com>
CC: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
CC: Sarah Sharp <sarah.a.sharp@linux.intel.com>
CC: Felipe Balbi <balbi@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>