gallium/inlines: remove atomic set from pipe_reference_init()
when an object is initialized with this, it should not be visible to any other threads or contexts, so there should be no need to use an atomic set here
at the time of this commit, there are only two callers in the tree which pass values != 1:
- zink uses a calculated number for framebuffer refcount on init (this is fine)
- aux/pb passes 0 on init (this is fine)