Use correct surface pressure to detect ceiling with Uemis Zurich

The dive data contains the surface pressure prior to the dive, and that is
what we need to compare p_amb_tol to, not the standard 1013mbar.

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>

dive.h

@@ -269,6 +269,7 @@ struct dive {
 	duration_t duration, surfacetime;
 	int visibility; /* 0 - 5 star rating */
 	temperature_t airtemp, watertemp;
+	pressure_t surface_pressure;
 	cylinder_t cylinder[MAX_CYLINDERS];
 	weightsystem_t weightsystem[MAX_WEIGHTSYSTEMS];
 	char *suit;