MIPS: ath79: fix AR933X WMAC reset code

The current code puts the built-in WMAC device of the
AR933X SoCs into reset instead of starting it. This
causes a hard lock on AR933X based boards when the
wireless driver tries to access the device.

Signed-off-by: Gabor Juhos <juhosg@openwrt.org>
Cc: stable@vger.kernel.org
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/3484/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>