leds: leds-lp5523: fix build warnings

This patch fixes build warnings as below:

drivers/leds/leds-lp5523.c: In function 'lp5523_selftest':
drivers/leds/leds-lp5523.c:496:18: warning: 'adc' may be used uninitialized in this function [-Wuninitialized]
drivers/leds/leds-lp5523.c:471:5: warning: 'vdd' may be used uninitialized in this function [-Wuninitialized]
drivers/leds/leds-lp5523.c: In function 'lp5523_probe':
drivers/leds/leds-lp5523.c:252:9: warning: 'status' may be used uninitialized in this function [-Wuninitialized]
drivers/leds/leds-lp5523.c:201:5: note: 'status' was declared here

If lp5523_read() returns an error, problems will happen. Thus,
when lp5523_read() returns an error, it should be handled.

Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Signed-off-by: Bryan Wu <cooloney@gmail.com>