mtd: spi-nor: Unprepare legacy controllers upon RWW wait interruption

All the parallel locking helpers (spi_nor_prep_and_lock(),
spi_nor_prep_and_lock_pe() and spi_nor_prep_and_lock_rd()) call
spi_nor_prep() then wait with a killable sleep. If the sleep gets
killed, we leave the controller in its prepared state.

Call ->unprepare() in these cases.

Fixes: 74df43b3f626 ("mtd: spi-nor: Enhance locking to support reads while writes")
Cc: stable@vger.kernel.org
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Reviewed-by: Michael Walle <mwalle@kernel.org>
Acked-by: Tudor Ambarus <tudor.ambarus@linaro.org>
Signed-off-by: Michael Walle <mwalle@kernel.org>