mtd: spi-nor: hisi: do not ignore clk_prepare_enable() failure

hisi_spi_nor_probe() ignores clk_prepare_enable() error code.
The patch fixes that.

Found by Linux Driver Verification project (linuxtesting.org).

Signed-off-by: Alexey Khoroshilov <khoroshilov@ispras.ru>
Acked-by: Marek Vasut <marek.vasut@gmail.com>
Signed-off-by: Cyrille Pitchen <cyrille.pitchen@atmel.com>