drivers: leds: leds-tca6507: check CONFIG_GPIOLIB whether defined for 'gpio_base'

Need check CONFIG_GPIOLIB whether defined, just like another area has
done within this file. Or can not pass compiling when CONFIG_GPIOLIB
disabled.

The related error (with allmodconfig for metag):

    CC [M]  drivers/leds/leds-tca6507.o
  drivers/leds/leds-tca6507.c: In function 'tca6507_led_dt_init':
  drivers/leds/leds-tca6507.c:731: error: 'struct tca6507_platform_data' has no member named 'gpio_base'

Signed-off-by: Chen Gang <gang.chen.5i5j@gmail.com>
Signed-off-by: Bryan Wu <cooloney@gmail.com>