nir: promote intrinsic_get_var() to helper

Useful in a few other places.. let's not copy-pasta

Signed-off-by: Rob Clark <robdclark@gmail.com>
Acked-by: Rob Clark <robdclark@gmail.com>
Acked-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
Acked-by: Dave Airlie <airlied@redhat.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>

src/compiler/nir/nir.h

@@ -1111,6 +1111,12 @@ typedef struct {
    nir_src src[];
 } nir_intrinsic_instr;
 
+static inline nir_variable *
+nir_intrinsic_get_var(nir_intrinsic_instr *intrin, unsigned i)
+{
+   return nir_deref_instr_get_variable(nir_src_as_deref(intrin->src[i]));
+}
+
 /**
  * \name NIR intrinsics semantic flags
  *