backlight: ipaq_micro: Fix sparse non static symbol warning

Fixes the following sparse warnings:

drivers/video/backlight/ipaq_micro_bl.c:73:24: warning:
 symbol 'micro_backlight_device_driver' was not declared. Should it be static?
Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Acked-by: Bryan Wu <cooloney@gmail.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

drivers/video/backlight/ipaq_micro_bl.c

@@ -70,7 +70,7 @@ static int micro_backlight_probe(struct platform_device *pdev)
 	return 0;
 }
 
-struct platform_driver micro_backlight_device_driver = {
+static struct platform_driver micro_backlight_device_driver = {
 	.driver = {
 		.name    = "ipaq-micro-backlight",
 	},