spi: stm32: defer probe for reset

Defer the probe operation when a reset controller device is expected
but have not yet been probed.

This change replaces use of devm_reset_control_get_exclusive() with
devm_reset_control_get_optional_exclusive() as reset controller is
optional which is now explicitly stated.
Signed-off-by: Alain Volmat <alain.volmat@foss.st.com>
Link: https://lore.kernel.org/r/1612551572-495-7-git-send-email-alain.volmat@foss.st.comSigned-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-stm32.c

@@ -1871,8 +1871,14 @@ static int stm32_spi_probe(struct platform_device *pdev)
 		goto err_clk_disable;
 	}
 
-	rst = devm_reset_control_get_exclusive(&pdev->dev, NULL);
-	if (!IS_ERR(rst)) {
+	rst = devm_reset_control_get_optional_exclusive(&pdev->dev, NULL);
+	if (rst) {
+		if (IS_ERR(rst)) {
+			ret = dev_err_probe(&pdev->dev, PTR_ERR(rst),
+					    "failed to get reset\n");
+			goto err_clk_disable;
+		}
+
 		reset_control_assert(rst);
 		udelay(2);
 		reset_control_deassert(rst);