intel/nir: Drop an unneeded lower_constant_initializers call

intel/nir: Drop an unneeded lower_constant_initializers call

Even though this is technically a step in the function inlining process
as laid out in nir_inline_functions.c, it's not really needed.  We
already have constant initializers lowered here and no new ones are
added by appending the softfp64 functions.

Reviewed-by: Matt Turner <mattst88@gmail.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>