drm/vc4: Fix resource leak in 'vc4_get_hang_state_ioctl()' in error handling path

If one 'drm_gem_handle_create()' fails, we leak somes handles and some
memory.

In order to fix it:
  - move the 'free(bo_state)' at the end of the function so that it is also
    called in the eror handling path. This has the side effect to also try
    to free it if the first 'kcalloc' fails. This is harmless.
  - add a new label, err_delete_handle, in order to delete already
    allocated handles in error handling path
  - remove the now useless 'err' label

The way the code is now written will also delete the handles if the
'copy_to_user()' call fails.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Reviewed-by: Eric Anholt <eric@anholt.net>
Link: http://patchwork.freedesktop.org/patch/msgid/20170512123803.1886-1-christophe.jaillet@wanadoo.fr