spi: Dont call master->setup if not populated

Currently the master->setup() is called unconditionally.
The assumption is that every driver need to implement this
callback. This encourages drivers to populate empty functions
to prevent crashing.

This patch prevents the call of master->setup() if it is not
populated.
Signed-off-by: NLaxman Dewangan <ldewangan@nvidia.com>
Signed-off-by: NMark Brown <broonie@opensource.wolfsonmicro.com>

drivers/spi/spi.c

@@ -1156,7 +1156,7 @@ EXPORT_SYMBOL_GPL(spi_busnum_to_master);
 int spi_setup(struct spi_device *spi)
 {
 	unsigned	bad_bits;
-	int		status;
+	int		status = 0;
 
 	/* help drivers fail *cleanly* when they need options
 	 * that aren't supported with their current master
@@ -1171,7 +1171,8 @@ int spi_setup(struct spi_device *spi)
 	if (!spi->bits_per_word)
 		spi->bits_per_word = 8;
 
-	status = spi->master->setup(spi);
+	if (spi->master->setup)
+		status = spi->master->setup(spi);
 
 	dev_dbg(&spi->dev, "setup mode %d, %s%s%s%s"
 				"%u bits/w, %u Hz max --> %d\n",