gpu: ion: fix kfree/list_del order

With CONFIG_SLUB_DEBUG_ON it would panic during
ion_alloc()
 ion_buffer_create()
   io_heap_drain_freelist()

Change-Id: I2a05c298e3941a1d5d0fa4ef33de208a818744bb
Signed-off-by: JP Abgrall <jpa@google.com>
Git-commit: ba6e9571a83c35eff6301bfae3471ce8e9cc7666
Git-repo: https://android.googlesource.com/kernel/common


Signed-off-by: Laura Abbott <lauraa@codeaurora.org>