clk: zynq: Remove unnecessary OOM message

As checkpatch suggests:
  WARNING: Possible unnecessary 'out of memory' message,
remove an error message after failing kmalloc() from the PLL driver.

Signed-off-by: Soren Brinkmann <soren.brinkmann@xilinx.com>
Signed-off-by: Mike Turquette <mturquette@linaro.org>