clk: Fix clk_hw_get_clk() when dev is NULL

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.

Fixes: 30d6f8c15d2c ("clk: add api to get clk consumer from clk_hw")
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://lore.kernel.org/r/20220225143534.405820-2-maxime@cerno.tech
Signed-off-by: Stephen Boyd <sboyd@kernel.org>