spi: nxp-fspi: Ensure width is respected in spi-mem operations

spi: nxp-fspi: Ensure width is respected in spi-mem operations

[ Upstream commit 007773e16a6f3f49d1439554078c3ba8af131998 ]

Make use of a core helper to ensure the desired width is respected
when calling spi-mem operators.

Otherwise only the SPI controller will be matched with the flash chip,
which might lead to wrong widths. Also consider the width specified by
the user in the device tree.

Fixes: a5356aef6a90 ("spi: spi-mem: Add driver for NXP FlexSPI controller")
Signed-off-by: Michael Walle <michael@walle.cc>
Link: https://lore.kernel.org/r/20191211195730.26794-1-michael@walle.cc
Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>