clk: renesas: Use IS_ERR() for pointers that cannot be NULL

clk: renesas: Use IS_ERR() for pointers that cannot be NULL

The use of IS_ERR_OR_NULL() suggests that "clk" can be a NULL pointer.
Hence smatch assumes so, and issues a "passing zero to 'PTR_ERR'"
warning.

At these checkpoints, "clk" always contains either a valid pointer, or
an error pointer (none of the functions called return NULL pointers).
Hence replace IS_ERR_OR_NULL() by IS_ERR().

Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Closes: https://lore.kernel.org/r/202408032025.ve2JMaoV-lkp@intel.com/
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Link: https://patch.msgid.link/81260328acb5c78e915ab04afad3901a31c16128.1758793709.git.geert+renesas@glider.be