hikey960: update name of recovery files (hisi-*)

The files used by "make recovery" have been renamed [1].

Link: [1] https://github.com/96boards-hikey/tools-images-hikey960/commit/b5ae2c13438e


Signed-off-by: Jerome Forissier <jerome.forissier@linaro.org>
Acked-by: Jens Wiklander <jens.wiklander@linaro.org>