fuchsia: Close VMO handles on unclaim_shared

VMO handles of address space memory are released at claim_shared()
and must be closed on unclaim_shared() to avoid memory leak.

Bug: fxbug.dev/124496
Test: 1. run and kill spinning-square-rs.cm
         ffx session add fuchsia-pkg://fuchsia.com/spinning-square-rs#meta/spinning-square-rs.cm
      2. check that there's no leaked VMOs (with parent from driver_host
	 of goldfish_address_space_device) in "fx shell memgraph -v".
Change-Id: I6c86186729294d65c94f007ae9ace462f8d69c8e
1 file changed