diracdsp_init: add missing ARCH_X86_64 check

That SIMD is still x86_64 only for now.

Signed-off-by: Rostislav Pehlivanov <atomnuker@gmail.com>

libavcodec/x86/diracdsp_init.c

@@ -192,6 +192,8 @@ void ff_diracdsp_init_x86(DiracDSPContext* c)
 
     if (EXTERNAL_SSE4(mm_flags)) {
         c->dequant_subband[1]         = ff_dequant_subband_32_sse4;
+#if ARCH_X86_64
         c->put_signed_rect_clamped[1] = ff_put_signed_rect_clamped_10_sse4;
+#endif
     }
 }