spi: Add "spi:" prefix to modalias attribute of spi devices

The modalias attribute of spi devices doesn't have the "spi:" prefix
that is used in the UEVENT and in spi device drivers.  This patch adds
the prefix so the modprobe can correctly match modules to devices.

Reported-by: David Daney <david.daney@cavium.com>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>

drivers/spi/spi.c

@@ -53,7 +53,7 @@ modalias_show(struct device *dev, struct device_attribute *a, char *buf)
 {
 	const struct spi_device	*spi = to_spi_device(dev);
 
-	return sprintf(buf, "%s\n", spi->modalias);
+	return sprintf(buf, "%s%s\n", SPI_MODULE_PREFIX, spi->modalias);
 }
 
 static struct device_attribute spi_dev_attrs[] = {