Input: ad7879 - add header file to fix ad7879.c build errors

Add header file to fix these build errors:

../drivers/input/touchscreen/ad7879.c: In function 'ad7879_parse_dt':
../drivers/input/touchscreen/ad7879.c:505:2: error: implicit declaration of function 'device_property_read_u32' [-Werror=implicit-function-declaration]
err = device_property_read_u32(dev, "adi,resistance-plate-x", &tmp);
^
../drivers/input/touchscreen/ad7879.c:512:2: error: implicit declaration of function 'device_property_read_u8' [-Werror=implicit-function-declaration]
device_property_read_u8(dev, "adi,first-conversion-delay",
^
../drivers/input/touchscreen/ad7879.c:521:2: error: implicit declaration of function 'device_property_read_bool' [-Werror=implicit-function-declaration]
ts->swap_xy = device_property_read_bool(dev, "touchscreen-swapped-x-y");
^

Signed-off-by: Randy Dunlap <[e-mail]>
Signed-off-by: Dmitry Torokhov <[e-mail]>

drivers/input/touchscreen/ad7879.c

···
 #include <linux/input.h>
 #include <linux/interrupt.h>
 #include <linux/irq.h>
+#include <linux/property.h>
 #include <linux/regmap.h>
 #include <linux/slab.h>
 #include <linux/gpio.h>