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

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.

Fixes: 45717804b75e ("clk: sunxi-ng: mp: introduce dual-divider clock")
Reviewed-by: Andre Przywara <andre.przywara@arm.com>
Link: https://patch.msgid.link/20250830170901.1996227-4-wens@kernel.org
Signed-off-by: Chen-Yu Tsai <wens@csie.org>