clk: sunxi-ng: mp: Fix dual-divider clock rate readback

In the Linux kernel, the following vulnerability has been resolved:

clk: sunxi-ng: mp: Fix dual-divider clock rate readback

When dual-divider clock support was introduced, the P divider offset was left out of the .recalc_rate readback function. This causes the clock rate to become bogus or even zero (possibly due to the P divider being 1, leading to a divide-by-zero).

Fix this by incorporating the P divider offset into the calculation.