clk: ingenic: jz4760: Update M/N/OD calculation algorithm

The previous algorithm was pretty broken.

- The inner loop had a '(m > m_max)' condition, and the value of 'm'
  would increase in each iteration;

- Each iteration would actually multiply 'm' by two, so it is not needed
  to re-compute the whole equation at each iteration;

- It would loop until (m & 1) == 0, which means it would loop at most
  once.

- The outer loop would divide the 'n' value by two at the end of each
  iteration. This meant that for a 12 MHz parent clock and a 1.2 GHz
  requested clock, it would first try n=12, then n=6, then n=3, then
  n=1, none of which would work; the only valid value is n=2 in this
  case.

Simplify this algorithm with a single for loop, which decrements 'n'
after each iteration, addressing all of the above problems.

Fixes: bdbfc029374f ("clk: ingenic: Add support for the JZ4760")
Cc: <stable@vger.kernel.org>
Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Link: https://lore.kernel.org/r/20221214123704.7305-1-paul@crapouillou.net
Signed-off-by: Stephen Boyd <sboyd@kernel.org>

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