Fix the gas mix parsing.
Fix the gas mix parsing.

The Suunto D9tx stores the gas mix definitions at a different offset
compared to the D4i and D6i.

henrik242/libdivecomputer,venkateshshukla/libdivecomputer,Poltsi/libdivecomputer-vms,venkateshshukla/libdivecomputer,josh-wambua/libdivecomputer,henrik242/libdivecomputer,glance-/libdivecomputer,josh-wambua/libdivecomputer,glance-/libdivecomputer