USB: cp210x.c: remove dbg() tracing calls

dbg() was used a lot a long time ago to trace code flow.  Now that we have
ftrace, this isn't needed at all, so remove these calls.

CC: Johan Hovold <jhovold@gmail.com>
CC: Preston Fick <preston.fick@silabs.com>
CC: Yuri Matylitski <ym@tekinsoft.com>
CC: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>