empathy-account-settings: fix CLAMP usage
empathy-account-settings: fix CLAMP usage

CLAMP syntax is (x, low, high), not (low, x, high). Also add some cast
to fix compiler warnings.

Distrotech/telepathy-account-widgets,GNOME/telepathy-account-widgets,Distrotech/telepathy-account-widgets,GNOME/telepathy-account-widgets,GNOME/telepathy-account-widgets