ovirt.te: Add type device_t

In commit 7a8aa86 and 8de7a60 we introduced device_t to sshd_t and snmpd_t.
However, we must declare device_t as well. This patch adds device_t.

Change-Id: I304cf80c4ff8989aca681f157883debc29c5132b
Signed-off-by: Douglas Schilling Landgraf <dougsland@redhat.com>