MIPS: ath79: Rename dev-ar913x-wmac.h to dev-wmac.h

The 'ar913x' part was removed from the common variable and function names,
so remove that from the relevant header file name as well.

Signed-off-by: Gabor Juhos <juhosg@openwrt.org>
Cc: Imre Kaloz <kaloz@openwrt.org>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/3033/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>