patches/openwrt: Turris 1.x: add LEDs driver: manually add io.h

Fixes:
drivers/leds/leds-turris-1x.c: In function 'turris1x_hwtrig_activate':
drivers/leds/leds-turris-1x.c:58:8: error: implicit declaration of function 'readb' [-Werror=implicit-function-declaration]
  val = readb(leds->regs + TURRIS1X_LED_SW_OVERRIDE_REG);
        ^~~~~
drivers/leds/leds-turris-1x.c:60:2: error: implicit declaration of function 'writeb'; did you mean 'wrtee'? [-Werror=implicit-function-declaration]
  writeb(val, leds->regs + TURRIS1X_LED_SW_OVERRIDE_REG);
  ^~~~~~
  wrtee
cc1: some warnings being treated as errors
make[6]: *** [scripts/Makefile.build:286: drivers/leds/leds-turris-1x.o] Error 1
make[5]: *** [scripts/Makefile.build:503: drivers/leds] Error 2