thermal: bug fix of check_valid_temp function

the greater-than symbol ">" in if state isn't valid and a file named "0" will
be created in this case, "-gt" should be used instead.

Signed-off-by: hongbo.zhang <hongbo.zhang@linaro.com>
diff --git a/include/thermal_functions.sh b/include/thermal_functions.sh
index 5b60698..f385ec1 100644
--- a/include/thermal_functions.sh
+++ b/include/thermal_functions.sh
@@ -42,7 +42,7 @@
     local descr="'$zone_name'/'$file' ='$temp_val'"
     log_begin "checking $descr"
 
-    if [ $temp_val > 0 ]; then
+    if [ $temp_val -gt 0 ]; then
         log_end "pass"
         return 0
     fi