soft-fp64/fadd: Reformat after previous commit

soft-fp64/fadd: Reformat after previous commit

Convert

   } else if (...) {
      ...
   } else {
      ...
   }

to

   } else {
      if (...) {
         ...
      } else {
         ...
      }
   }

Not doing this reformatting in the previous commit makes the previous
commit easier to review, and doing it before the next commit makes the
next commit easier to review.

Reviewed-by: Matt Turner <mattst88@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4142>