spi: cadence-quadspi: Wait at least 500 ms for direct reads

When performing a direct read via DMA the timeout for completion is set
equal to the read length. This is fine for larger reads. For a small
read like the Read Status Register command, the timeout would be 1 or 2
milliseconds. This is not enough to cover the overhead needed in setting
up DMA.

Make sure the timeout is at least 500 ms to allow DMA ample time to
finish. For reads larger than 500 bytes, the timeout will continue to be
equal to the read length.

Signed-off-by: Pratyush Yadav <p.yadav@ti.com>
Reported-by: kernel test robot <lkp@intel.com>
Link: https://lore.kernel.org/r/20201222184425.7028-7-p.yadav@ti.com
Signed-off-by: Mark Brown <broonie@kernel.org>