spi: omap2-mcspi: Fix the IS_ERR() bug for devm_clk_get_optional_enabled()

The devm_clk_get_optional_enabled() function returns error
pointers(PTR_ERR()). So use IS_ERR() to check it.

Verified on K3-J7200 EVM board, without clock node mentioned
in the device tree.

Signed-off-by: Purushothama Siddaiah <psiddaiah@mvista.com>
Reviewed-by: Corey Minyard <cminyard@mvista.com>
Link: https://patch.msgid.link/20241205070426.1861048-1-psiddaiah@mvista.com
Signed-off-by: Mark Brown <broonie@kernel.org>

Author: psiddaiah

drivers/spi/spi-omap2-mcspi.c

@@ -1561,10 +1561,10 @@ static int omap2_mcspi_probe(struct platform_device *pdev)
 	}
 
 	mcspi->ref_clk = devm_clk_get_optional_enabled(&pdev->dev, NULL);
-	if (mcspi->ref_clk)
-		mcspi->ref_clk_hz = clk_get_rate(mcspi->ref_clk);
-	else
+	if (IS_ERR(mcspi->ref_clk))
 		mcspi->ref_clk_hz = OMAP2_MCSPI_MAX_FREQ;
+	else
+		mcspi->ref_clk_hz = clk_get_rate(mcspi->ref_clk);
 	ctlr->max_speed_hz = mcspi->ref_clk_hz;
 	ctlr->min_speed_hz = mcspi->ref_clk_hz >> 15;