intel/compiler: Don't copy prop source mods into PICK_HIGH_32BIT

intel/compiler: Don't copy prop source mods into PICK_HIGH_32BIT

VEC4_OPCODE_PICK_HIGH_32BIT performs 32-bit UD access on a 64-bit DF
value.  abs and negate make sense on DF, but break entirely when
trying to access pieces of the value as unsigned integer dwords.

Fixes an fsign Piglit test on Ivybridge:
tests/spec/arb_gpu_shader_fp64/execution/built-in-functions/vs-sign-neg-abs

It had regressed when I removed nir_lower_to_source_modifiers, as that
caused us to start generating different code which provoked this bug.

Fixes: b7c47c4f7cf ("intel/compiler: Drop nir_lower_to_source_mods() and related handling.")
Closes: https://gitlab.freedesktop.org/mesa/mesa/-/issues/2817
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Reviewed-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4691>