init: fix to set sd device label correctly for FS

The sysfs node of sd blk_device is /sys/fs/f2fs/sd-<num>, we shouldn't
skip partition number at this time.

Bug: 189257443
Test: access sd-<num> sysfs correctly
Signed-off-by: Guo Weichao <guoweichao@oppo.com>
Signed-off-by: Huang Jianan <huangjianan@oppo.com>
Change-Id: Ibcd7bb265f8fca9cd26f8770403f1bafad433acb