spi: sun6i: disable/unprepare clocks on remove

sun6i_spi_probe() uses sun6i_spi_runtime_resume() to prepare/enable
clocks, so sun6i_spi_remove() should use sun6i_spi_runtime_suspend() to
disable/unprepare them if we're not suspended.
Replacing pm_runtime_disable() by pm_runtime_force_suspend() will ensure
that sun6i_spi_runtime_suspend() is called if needed.

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

Fixes: 3558fe90 (spi: sunxi: Add Allwinner A31 SPI controller driver)
Signed-off-by: Tobias Jordan <Tobias.Jordan@elektrobit.com>
Acked-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Mark Brown <broonie@kernel.org>