clk: sprd: add missing kfree

clk: sprd: add missing kfree

The number of config registers for different pll clocks probably are not
same, so we have to use malloc, and should free the memory before return.

Fixes: edb8737dcd4b ("clk: sprd: add adjustable pll support")
Signed-off-by: Chunyan Zhang <chunyan.zhang@unisoc.com>
Signed-off-by: Chunyan Zhang <zhang.lyra@gmail.com>
Link: https://lkml.kernel.org/r/20190905103009.27166-1-zhang.lyra@gmail.com
Signed-off-by: Stephen Boyd <sboyd@kernel.org>