nir: Allocate nir_tex_instr::sources out of the instruction itself.
nir: Allocate nir_tex_instr::sources out of the instruction itself.

The lifetime of the sources array needs to be match the nir_tex_instr
itself.  So, allocate it using the instruction itself as the context.

Signed-off-by: Kenneth Graunke <bd2562f754ec92342f93f61c25d731e290a2ffa8@whitecape.org>
Reviewed-by: Jason Ekstrand <b186559eaedf698788888c8a2559b4efb4db10d6@intel.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler