clk: qoriq: fix memory leak

If get_pll_div() fails we exited by returning NULL but we missed
releasing hwc.

Signed-off-by: Sudip Mukherjee <sudip@vectorindia.org>
Fixes: 0dfc86b3 ("clk: qoriq: Move chip-specific knowledge into driver")
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>