spi: Fix SPI slave probe failure

spi: Fix SPI slave probe failure

BugLink: https://bugs.launchpad.net/bugs/2075154
[ Upstream commit 2c1b7bbe253986619fa5623a13055316e730e746 ]

While adding a SPI device, the SPI core ensures that multiple logical CS
doesn't map to the same physical CS. For example, spi->chip_select[0] !=
spi->chip_select[1] and so forth. However, unlike the SPI master, the SPI
slave doesn't have the list of chip selects, this leads to probe failure
when the SPI controller is configured as slave. Update the
__spi_add_device() function to perform this check only if the SPI
controller is configured as master.

Fixes: 4d8ff6b0991d ("spi: Add multi-cs memories support in SPI core")
Signed-off-by: Amit Kumar Mahapatra <amit.kumar-mahapatra@amd.com>
Link: https://msgid.link/r/20240617153052.26636-1-amit.kumar-mahapatra@amd.com
Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Manuel Diewald <manuel.diewald@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>