spice-session: Simplify spice_session_get_mm_time formula
spice-session: Simplify spice_session_get_mm_time formula

Instead of keeping 2 fields for the conversion monotonic time ->
multimedia time compute a single offset.

Signed-off-by: Frediano Ziglio <55d48b080b2e443e395cde84d2c83b135a4ff48e@redhat.com>
Acked-by: Uri Lublin <0332784c07b6f27b46541214503bc0da50f0f291@redhat.com>

flexVDI/spice-gtk,flexVDI/spice-gtk