spi: Make spi_delay_exec() warn if called from atomic context

If the delay used is long enough the spi_delay_exec() will use a sleeping
function to implement it. Add a might_sleep() here to help avoid callers
using this from an atomic context and running into problems at runtime on
other systems.

Suggested-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
Signed-off-by: Mark Brown <broonie@kernel.org>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20200522155005.46099-1-broonie@kernel.org
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi.c

@@ -1160,6 +1160,8 @@ int spi_delay_exec(struct spi_delay *_delay, struct spi_transfer *xfer)
 {
 	int delay;
 
+	might_sleep();
+
 	if (!_delay)
 		return -EINVAL;