The `init.name` could be NULL. Add missing check in the
raspberrypi_clk_register().
This is similar to commit 3027e7b15b02
("ice: Fix some null pointer dereference issues in ice_ptp.c").
Besides, bcm2835_register_pll_divider() under the same directory also
has a very similar check.
Signed-off-by: Chenyuan Yang <chenyuan0y@xxxxxxxxx>