USB: garmin_gps.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: Andrew Morton <akpm@linux-foundation.org>
CC: Rusty Russell <rusty@rustcorp.com.au>
CC: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>