staging: tidspbridge: gen: simplify and clean up

There is recently added hex_to_bin() kernel's method which we could use
instead of custom long function.

Signed-off-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Cc: Ohad Ben-Cohen <ohad@wizery.com>
Cc: linux-omap@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>