gpio: crystalcove: Fix implicit declaration of function 'seq_printf' error

drivers/gpio/gpio-crystalcove.c: In function 'crystalcove_gpio_dbg_show':
drivers/gpio/gpio-crystalcove.c:286:3: error: implicit declaration of function 'seq_printf'
seq_printf(s, " gpio-%-2d %s %s %s %s ctlo=%2x,%s %s %s\n",

Reported-by: Stephen Rothwell <[e-mail]>
Acked-by: Alexandre Courbot <[e-mail]>
Signed-off-by: Lee Jones <[e-mail]>

drivers/gpio/gpio-crystalcove.c

···
 #include <linux/interrupt.h>
 #include <linux/platform_device.h>
 #include <linux/gpio.h>
+#include <linux/seq_file.h>
 #include <linux/bitops.h>
 #include <linux/regmap.h>
 #include <linux/mfd/intel_soc_pmic.h>