spi: use new `spi_transfer_delay_exec` helper where straightforward

For many places in the spi drivers, using the new `spi_transfer_delay`
helper is straightforward.
It's just replacing:
```
  if (t->delay_usecs)
     udelay(t->delay_usecs);
```
with `spi_transfer_delay(t)` which handles both `delay_usecs` and the new
`delay` field.

This change replaces in all places (in the spi drivers)  where this change
is simple.

Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
Link: https://lore.kernel.org/r/20190926105147.7839-10-alexandru.ardelean@analog.com
Signed-off-by: Mark Brown <broonie@kernel.org>
diff --git a/drivers/spi/spi-sc18is602.c b/drivers/spi/spi-sc18is602.c
index 11acddc..5497eeb 100644
--- a/drivers/spi/spi-sc18is602.c
+++ b/drivers/spi/spi-sc18is602.c
@@ -211,8 +211,7 @@ static int sc18is602_transfer_one(struct spi_master *master,
 		}
 		status = 0;
 
-		if (t->delay_usecs)
-			udelay(t->delay_usecs);
+		spi_transfer_delay_exec(t);
 	}
 	m->status = status;
 	spi_finalize_current_message(master);