CVE-2022-49187: NULL Pointer Dereference

In the Linux kernel, the following vulnerability has been resolved:

clk: Fix clk_hw_get_clk() when dev is NULL

Any registered clk_core structure can have a NULL pointer in its dev field. While never actually documented, this is evidenced by the wide usage of clk_register and clk_hw_register with a NULL device pointer, and the fact that the core of_clk_hw_register() function also passes a NULL device pointer.

A call to clk_hw_get_clk() on a clk_hw struct whose clk_core is in that case will result in a NULL pointer derefence when it calls dev_name() on that NULL device pointer.

Add a test for this case and use NULL as the dev_id if the device pointer is NULL.