AMDGPU: Match fract pattern with swapped edge case check (#189081)

A fract implementation can equivalently be written as
  r = fmin(x - floor(x))
  r = isnan(x) ? x : r;
  r = isinf(x) ? 0.0 : r;

or:
  r = fmin(x - floor(x));
  r = isinf(x) ? 0.0 : r;
  r = isnan(x) ? x : r;

Previously this only matched the previous form. Match
the case where the isinf check is the inner clamp. There are
a few more ways to write this pattern (e.g., move the clamp of
infinity to the input) but I haven't encountered that in the wild.

The existing code seems to be trying too hard to match noncanonical
variants of the pattern. Only handles the result that all 4 permutations
of compare and select produce out of instcombine.