spi: spidev_test: Warn when the mode is not the requested mode

spi: spidev_test: Warn when the mode is not the requested mode

Print a warning if the device mode doesn't match the requested mode.
The user doesn't enter the mode in hex so it isn't obvious when
setting the mode succeeds that the mode isn't the requested mode.  The
kernel logs a message, it will be more visible if the test also prints
a warning.  I was testing --quad, which is unsupported, but doesn't
cause the mode request to fail.

Signed-off-by: David Fries <David@Fries.net>
Link: https://lore.kernel.org/r/YqbNnSGtWHe/GG7w@spacedout.fries.net
Signed-off-by: Mark Brown <broonie@kernel.org>