leds: sc27xx: Fix return value check in sc27xx_led_probe()

In case of error, the function dev_get_regmap() returns NULL pointer not
ERR_PTR(). The IS_ERR() test in the return value check should be
replaced with NULL test.

Fixes: e081c49e ("leds: Add Spreadtrum SC27xx breathing light controller driver")
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: Jacek Anaszewski <jacek.anaszewski@gmail.com>