ar71xx: fix build error

This fixes a build error introduced in r49193.

This closes #22230

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>

SVN-Revision: 49194

target/linux/ar71xx/files/arch/mips/ath79/mach-om5pacv2.c

@@ -11,6 +11,7 @@
  */
 
 #include <linux/gpio.h>
+#include <linux/version.h>
 #if LINUX_VERSION_CODE < KERNEL_VERSION(4,4,0)
 #include <linux/mdio-gpio.h>
 #else

target/linux/ar71xx/files/arch/mips/ath79/mach-rb4xx.c

@@ -11,6 +11,7 @@
 
 #include <linux/platform_device.h>
 #include <linux/irq.h>
+#include <linux/version.h>
 #if LINUX_VERSION_CODE < KERNEL_VERSION(4,4,0)
 #include <linux/mdio-gpio.h>
 #else