isl_scheduler.c: node_update_vmap: extract out extract_linear_schedule
isl_scheduler.c: node_update_vmap: extract out extract_linear_schedule

This is a minor code clean-up.

Signed-off-by: Sven Verdoolaege <235c10dd23b819f81cdc9756a251746bc184cab6@gmail.com>

Meinersbur/isl,Meinersbur/isl,Meinersbur/isl,Meinersbur/isl