glsl: Don't use MOD_TO_FRACT lowering on GLSL 1.30's % operator.

glsl: Don't use MOD_TO_FRACT lowering on GLSL 1.30's % operator.

MOD_TO_FRACT was designed to lower the GLSL 1.20 mod() function, which
operates on floating point values.  However, we also use ir_binop_mod
for GLSL 1.30's % operator, which operates on integers.

For now, make MOD_TO_FRACT only apply to floating-point mod operations.
In the future, we may want to add a lowering pass for integer-based mod.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Eric Anholt <eric@anholt.net>