anv: gem-stubs: return a valid fd got anv_gem_userptr()

Fixes invalid close(-1) in the unit tests.

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Cc: <mesa-stable@lists.freedesktop.org>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
(cherry picked from commit da2d67fc3b)

src/intel/vulkan/anv_gem_stubs.c

@@ -68,7 +68,13 @@ anv_gem_munmap(void *p, uint64_t size)
 uint32_t
 anv_gem_userptr(struct anv_device *device, void *mem, size_t size)
 {
-   return -1;
+   int fd = os_create_anonymous_file(size, "fake bo");
+   if (fd == -1)
+      return 0;
+
+   assert(fd != 0);
+
+   return fd;
 }
 
 int