clk: zynq: Prevent null pointer dereference caused by kmalloc failure

In the Linux kernel, the following vulnerability has been resolved: clk: zynq: Prevent null pointer dereference caused by kmalloc failure The kmalloc() in zynq_clk_setup() will return null if the physical memory has run out. As a result, if we use snprintf() to write data to the null address, the null pointer dereference bug will happen. This patch uses a stack variable to replace the kmalloc().