thermal: add description for integral_cutoff unit

Add more explicitly description for unit of integral_cutoff which used
by power allocator governor.

Signed-off-by: Leo Yan <leo.yan@linaro.org>
Acked-by: Javi Merino <javi.merino@arm.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
diff --git a/Documentation/thermal/sysfs-api.txt b/Documentation/thermal/sysfs-api.txt
index 10f062e..8c745c8 100644
--- a/Documentation/thermal/sysfs-api.txt
+++ b/Documentation/thermal/sysfs-api.txt
@@ -364,6 +364,7 @@
 	accumulates error when temperature is above the desired
 	temperature trip point. For more information see
 	Documentation/thermal/power_allocator.txt
+	Unit: millidegree Celsius
 	RW, Optional
 
 slope