USB: qcserial.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: Thomas Tuttle <ttuttle@chromium.org>
CC: Paul Gortmaker <paul.gortmaker@windriver.com>
CC: Rusty Russell <rusty@rustcorp.com.au>
CC: Rigbert Hamisch <rigbert@gmx.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>