clk: fix incorrect usage of ENOSYS

ENOSYS is special and should only be used for incorrect syscall number.
It does not seem to be the case here.

Reported by checkpatch.pl while working on clock protection.
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Tested-by: Quentin Schulz <quentin.schulz@free-electrons.com>
Tested-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Acked-by: Michael Turquette <mturquette@baylibre.com>
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Signed-off-by: Michael Turquette <mturquette@baylibre.com>
Link: lkml.kernel.org/r/20171201215200.23523-2-jbrunet@baylibre.com

drivers/clk/clk.c

@@ -1888,7 +1888,7 @@ static int clk_core_set_parent(struct clk_core *core, struct clk_core *parent)
 
 	/* verify ops for for multi-parent clks */
 	if ((core->num_parents > 1) && (!core->ops->set_parent)) {
-		ret = -ENOSYS;
+		ret = -EPERM;
 		goto out;
 	}