phosphor-hwmon: fixing starting occ sensor

On P9 the occ device has `:` in path, and it needs to be converted to
`--` while starting hwmon service.

The commit 2f714db14 accidentally removes the convertion, and cause P9's
occ hwmon sensor are not started.

This commit fixes the issue by converting `:` to `--` first.

Tested: Verify the occ hwmon sensors are started on Romulus

Change-Id: Ic9e40066936c86076c38d11353fbb4f8abbebd13
Signed-off-by: Lei YU <mine260309@gmail.com>
diff --git a/recipes-phosphor/sensors/phosphor-hwmon/start_hwmon.sh b/recipes-phosphor/sensors/phosphor-hwmon/start_hwmon.sh
index cf72528..c1ec42e 100755
--- a/recipes-phosphor/sensors/phosphor-hwmon/start_hwmon.sh
+++ b/recipes-phosphor/sensors/phosphor-hwmon/start_hwmon.sh
@@ -17,7 +17,7 @@
     fi
 fi
 
+path="${path//:/--}"
 path="${path//-/\\x2d}"
-path="${path//:/\\x3a}"
 
 systemctl $action 'xyz.openbmc_project.Hwmon@'$path'.service'