spi: spi-mem: Fix typo (of -> or)

In this instance, "or" makes more sense than "of", so I guess that "or"
was intended and "of" was a typo.

Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Link: https://lore.kernel.org/r/20221008151459.1421406-1-j.neuschaefer@gmx.net
Signed-off-by: Mark Brown <broonie@kernel.org>