MIPS: RB532: Use hex_to_bin()

Remove custom implementation of hex_to_bin().

Signed-off-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-mips@linux-mips.org
To: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/1580/


Acked-by: Florian Fainelli <florian@openwrt.org>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>