Pixelstats: add block layer stats length

The block layer stats format is changing
time by time. This can pass the correct
length by project.

Bug: 219860725
Test: reboot and check log
Change-Id: Idf3a9a8e22d0a6f0645ac7e9ef8cb7b971aea16c
diff --git a/pixelstats/service.cpp b/pixelstats/service.cpp
index b327477..6218eeb 100644
--- a/pixelstats/service.cpp
+++ b/pixelstats/service.cpp
@@ -28,6 +28,7 @@
 using android::hardware::google::pixel::SysfsCollector;
 using android::hardware::google::pixel::UeventListener;
 
+#define BLOCK_STATS_LENGTH 11
 #define MAXIM_DIR(filename) "/sys/class/power_supply/maxfg/" #filename
 #define UFSHC_PATH(filename) "/dev/sys/block/bootdevice/" #filename
 #define UFSHC_HEALTH_PATH(filename) "/dev/sys/block/bootdevice/health/" #filename