spi: spi-tegra20-flash: don't check 'delay_usecs' field for spi transfer

spi: spi-tegra20-flash: don't check 'delay_usecs' field for spi transfer

The 'delay_usecs' field was handled for backwards compatibility in case
there were some users that still configured SPI delay transfers with
this field.

They should all be removed by now. So we can remove the 'delay_usecs'
handling in this driver.

Signed-off-by: Alexandru Ardelean <aardelean@deviqon.com>
Link: https://lore.kernel.org/r/20210308145502.1075689-6-aardelean@deviqon.com
Signed-off-by: Mark Brown <broonie@kernel.org>