clk: sprd: fix to get a correct ibias of pll

The current driver is getting a wrong ibias index of pll clocks from
number 1. This patch fix that issue, then getting ibias index from 0.

Fixes: 3e37b005

 ("clk: sprd: add adjustable pll support")
Signed-off-by: Chunyan Zhang <chunyan.zhang@unisoc.com>
Link: https://lkml.kernel.org/r/20200330021640.14133-1-zhang.lyra@gmail.com
Signed-off-by: Stephen Boyd <sboyd@kernel.org>