spa: clamp required alignment to cpu alignment

pipewire will allocate buffers aligned to the max alignment required for
the CPU. Take this into account and don't expect larger alignment.

Fixes a warning in mixer-dsp when the CPU max alignment is 16 but the
plugin requires 32 bytes alignment for the AVX2 path (that would never
be chosen on the CPU).

See #2074

spa/plugins/audioconvert/volume-ops.h

@@ -56,6 +56,8 @@ void volume_##name##_##arch(struct volume *vol,		\
 		const void * SPA_RESTRICT src,		\
 		float volume, uint32_t n_samples);
 
+#define VOLUME_OPS_MAX_ALIGN	16
+
 DEFINE_FUNCTION(f32, c);
 
 #if defined (HAVE_SSE)