leds: lm3532: select regmap I2C API

Regmap APIs should be selected, otherwise link can fail

ERROR: modpost: "__devm_regmap_init_i2c" [drivers/leds/leds-lm3532.ko] undefined!

Fixes: bc1b8492 ("leds: lm3532: Introduce the lm3532 LED driver")
Cc: Dan Murphy <dmurphy@ti.com>
Signed-off-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Pavel Machek <pavel@ucw.cz>

drivers/leds/Kconfig

@@ -199,6 +199,7 @@ config LEDS_LM3530
 
 config LEDS_LM3532
 	tristate "LCD Backlight driver for LM3532"
+	select REGMAP_I2C
 	depends on LEDS_CLASS
 	depends on I2C
 	help