spi: docs: adjust summary to CONFIG_SYSFS_DEPRECATED removal

With commit 721da5ce ("driver core: remove CONFIG_SYSFS_DEPRECATED and
CONFIG_SYSFS_DEPRECATED_V2"), ./scripts/checkkconfigsymbols.py indicated
an unresolved reference to the config SYSFS_DEPRECATED in the SPI summary
documentation.

Simply, delete the sentence referring to the removed config there. Also
update the documentation, as these sys/class entries should always be
symlinks, as the commit message of the commit above suggests.

Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://lore.kernel.org/r/20230314075609.5232-1-lukas.bulwahn@gmail.com


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