ar71xx: spi-rb4xx fix.

In new kernels we should use clk_prepare_enable instead of clk_enable
since clk_enable does not make proper initialization that leads
to rise WARN_ON messages and not working spi bus on the device.

Signed-off-by: Sergey Sergeev <adron@yapic.net>

target/linux/ar71xx/files/drivers/spi/spi-rb4xx.c

@@ -413,7 +413,7 @@ static int rb4xx_spi_probe(struct platform_device *pdev)
 		goto err_put_master;
 	}
 
-	err = clk_enable(rbspi->ahb_clk);
+	err = clk_prepare_enable(rbspi->ahb_clk);
 	if (err)
 		goto err_clk_put;