spi: s3c64xx: Fix pm_runtime_get_sync() return value check

If the device is already in a runtime PM enabled state
pm_runtime_get_sync() will return 1, so a test for negative
value should be used to check for errors.

Without this patch there are seen errors like:

[    8.540000] s3c64xx-spi 13930000.spi: Failed to enable device: 1
[    8.545000] spi_master spi1: failed to prepare transfer hardware

Likely because the driver uses synchronous API to runtime enable
the device and asynchronous one to disable it.
Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Mark Brown <broonielinaro.org>
Cc: stable@vger.kernel.org

drivers/spi/spi-s3c64xx.c

@@ -444,7 +444,7 @@ static int s3c64xx_spi_prepare_transfer(struct spi_master *spi)
 	}
 
 	ret = pm_runtime_get_sync(&sdd->pdev->dev);
-	if (ret != 0) {
+	if (ret < 0) {
 		dev_err(dev, "Failed to enable device: %d\n", ret);
 		goto out_tx;
 	}