spi: Add check for 8-bit transfer with 8 IO mode support

The current SPI framework does not verify if the SPI device supports
8 IO mode when doing an 8-bit transfer. This patch adds a check to
ensure that if the transfer tx_nbits or rx_nbits is 8, the SPI mode must
support 8 IO. If not, an error is returned, preventing undefined behavior.

Fixes: d6a711a8 ("spi: Fix OCTAL mode support")
Cc: stable@vger.kernel.org
Signed-off-by: Cheng Ming Lin <chengminglin@mxic.com.tw>
Link: https://patch.msgid.link/20250714031023.504752-1-linchengming884@gmail.com


Signed-off-by: Mark Brown <broonie@kernel.org>