mosquitto: clarify that patch hash is locally calculated

Commit e51d69a3b (mosquitto: specify that hash is taken from upstream)
changed the .hash description header, but the upstream hash only applies
to the tarball, not the patch.

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/mosquitto/mosquitto.hash

@@ -1,3 +1,4 @@
 # From http://www.eclipse.org/downloads/download.php?file=/mosquitto/source/mosquitto-1.4.12.tar.gz
 sha512  75e6105498869ab13265df7a0bea6052c014d59d0c0efb61162d8257d34c0153fce32130e84c28e99fd494f374949aac5e01c19f7439c2eea575b52ef1179c3c  mosquitto-1.4.12.tar.gz
+# Locally computed:
 sha256  06abd1206e548ac2378dd96f5434cb3e40ed77cecb6a9c37fbabab0b0f1360e5  mosquitto-1.4.x_cve-2017-9868.patch