mfd: ti_am335x_tscadc: Don't search the tree for our clock

There is a single clock available in our node, which is named
"fck". The clock handler then points to adc_tsc_fck but no need to point
directly to it and do a full tree search.
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20211015081506.933180-15-miquel.raynal@bootlin.com

drivers/mfd/ti_am335x_tscadc.c

@@ -206,7 +206,7 @@ static	int ti_tscadc_probe(struct platform_device *pdev)
 	 * This frequency is valid since TSC_ADC_SS controller design
 	 * assumes the OCP clock is at least 6x faster than the ADC clock.
 	 */
-	clk = devm_clk_get(&pdev->dev, "adc_tsc_fck");
+	clk = devm_clk_get(&pdev->dev, NULL);
 	if (IS_ERR(clk)) {
 		dev_err(&pdev->dev, "failed to get TSC fck\n");
 		err = PTR_ERR(clk);