mtd: st_spi_fsm: Add a clk_disable_unprepare() in .probe()'s error path

For all but one error path clk_disable_unprepare() is already there. Add
it to the one location where it's missing.

Fixes: 481815a6 ("mtd: st_spi_fsm: Handle clk_prepare_enable/clk_disable_unprepare.")
Fixes: 69d5af8d ("mtd: st_spi_fsm: Obtain and use EMI clock")
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20220607152458.232847-2-u.kleine-koenig@pengutronix.de

drivers/mtd/devices/st_spi_fsm.c

@@ -2115,10 +2115,12 @@ static int stfsm_probe(struct platform_device *pdev)
 		(long long)fsm->mtd.size, (long long)(fsm->mtd.size >> 20),
 		fsm->mtd.erasesize, (fsm->mtd.erasesize >> 10));
 
-	return mtd_device_register(&fsm->mtd, NULL, 0);
-
+	ret = mtd_device_register(&fsm->mtd, NULL, 0);
+	if (ret) {
 err_clk_unprepare:
-	clk_disable_unprepare(fsm->clk);
+		clk_disable_unprepare(fsm->clk);
+	}
+
 	return ret;
 }