clk: h8300: fix error handling in h8s2678_pll_clk_setup()

The error handling was a bit messy and buggy.  It freed "pll_clock" then
dereferenced it, and then freed it again.  I've re-written it in normal
kernel style.

Fixes: 42ff8e8008c8 ('h8300: clock driver')
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>