BatteryService(jni): properly handle read's return value

Change-Id: I10f5cf3728424e7f5a0c1b460049102fd00a6246
Signed-off-by: Dima Zavin <dima@android.com>

services/jni/com_android_server_BatteryService.cpp

@@ -141,10 +141,10 @@ static int readFromFile(const char* path, char* buf, size_t size)
         return -1;
     }
     
-    size_t count = read(fd, buf, size);
+    ssize_t count = read(fd, buf, size);
     if (count > 0) {
-        count = (count < size) ? count : size - 1;
-        while (count > 0 && buf[count-1] == '\n') count--;
+        while (count > 0 && buf[count-1] == '\n')
+            count--;
         buf[count] = '\0';
     } else {
         buf[0] = '\0';