spidev: Simplify SPI_IOC_RD_MODE* cases in spidev_ioctl()

The temporary variable tmp is not used outside of the
SPI_IOC_RD_MODE* cases, hence we can optimize its use.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Lukas Wunner <lukas@wunner.de>
Reviewed-by: Alexander Sverdlin <alexander.sverdlin@siemens.com>
Link: https://lore.kernel.org/r/20230824162209.2890440-4-andriy.shevchenko@linux.intel.com


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