clk: pxa: add a check for the return value of kzalloc()

clk: pxa: add a check for the return value of kzalloc()

kzalloc() is a memory allocation function which can return NULL when
some internal memory errors happen. So it is better to check it to
prevent potential wrong memory access.

Signed-off-by: Xiaoke Wang <xkernel.wang@foxmail.com>
Link: https://lore.kernel.org/r/tencent_2B9817738F38B02844C245946EFF3B407E09@qq.com
Signed-off-by: Stephen Boyd <sboyd@kernel.org>