clk: Skip clk provider registration when np is NULL

commit 6579c8d97ad7 ("clk: Mark fwnodes when their clock provider is added")
revealed that clk/bcm/clk-raspberrypi.c driver calls
devm_of_clk_add_hw_provider(), with a NULL dev->of_node, which resulted in a
NULL pointer dereference in of_clk_add_hw_provider() when calling
fwnode_dev_initialized().

Returning 0 is reducing the if conditions in driver code and is being
consistent with the CONFIG_OF=n inline stub that returns 0 when CONFIG_OF
is disabled. The downside is that drivers will maybe register clkdev lookups
when they don't need to and waste some memory.

Fixes: 6579c8d97ad7 ("clk: Mark fwnodes when their clock provider is added")
Fixes: 3c9ea42802a1 ("clk: Mark fwnodes when their clock provider is added/removed")
Reported-by: Marek Szyprowski <[e-mail]>
Tested-by: Guenter Roeck <[e-mail]>
Tested-by: Nathan Chancellor <[e-mail]>
Reviewed-by: Stephen Boyd <[e-mail]>
Reviewed-by: Saravana Kannan <[e-mail]>
Reviewed-by: Nicolas Saenz Julienne <[e-mail]>
Signed-off-by: Tudor Ambarus <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/clk/clk.c

···
 	struct of_clk_provider *cp;
 	int ret;
 
+	if (!np)
+		return 0;
+
 	cp = kzalloc(sizeof(*cp), GFP_KERNEL);
 	if (!cp)
 		return -ENOMEM;
···
 {
 	struct of_clk_provider *cp;
 	int ret;
+
+	if (!np)
+		return 0;
 
 	cp = kzalloc(sizeof(*cp), GFP_KERNEL);
 	if (!cp)
···
 void of_clk_del_provider(struct device_node *np)
 {
 	struct of_clk_provider *cp;
+
+	if (!np)
+		return;
 
 	mutex_lock(&of_clk_mutex);
 	list_for_each_entry(cp, &of_clk_providers, link) {