spi: spidev: prevent spidev->speed_hz from being zero

spi: spidev: prevent spidev->speed_hz from being zero

A zero value for spi->max_speed_hz or spidev->speed_hz does not make
sense and trying to set that can lead to divide by zero crashes in
a some of the drivers.

drivers/spi/spi-s3c64xx.c:874 s3c64xx_spi_setup() error: potential divide by zero bug '/ spi->max_speed_hz'.
drivers/spi/spi-fsl-dspi.c:613 hz_to_spi_baud() error: potential divide by zero bug '/ speed_hz'.
drivers/spi/spi-xlp.c:146 xlp_spi_setup() error: potential divide by zero bug '/ (spi->max_speed_hz)'.
drivers/spi/spi-orion.c:162 orion_spi_baudrate_set() error: potential divide by zero bug '/ speed'.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Link: https://lore.kernel.org/r/20220125065202.GA8807@kili
Signed-off-by: Mark Brown <broonie@kernel.org>