According to Reference Manual:
 000b - Divide by 1
 001b - Divide by 1
 010b - Divide by 2
 011b - Divide by 3
 100b - Divide by 4
 101b - Divide by 5
 110b - Divide by 6
 111b - Divide by 7

So only need increase rdiv by 1 when the register value is 0.

Fixes: 1b26cb8a ("clk: imx: support fracn gppll")
Signed-off-by: Peng Fan <peng.fan@nxp.com>
Reviewed-by: Jacky Bai <ping.bai@nxp.com>
Reviewed-by: Abel Vesa <abel.vesa@linaro.org>
Link: https://lore.kernel.org/r/20220609132902.3504651-7-peng.fan@oss.nxp.comSigned-off-by: Abel Vesa <abel.vesa@linaro.org>