nir: cleanup oversized arrays in nir_swizzle calls

nir: cleanup oversized arrays in nir_swizzle calls

There are no fixed sized array arguments in C, those are simply pointers
to unsized arrays and as the size is passed in anyway, just rely on that.

where possible calls are replaced by nir_channel and nir_channels.

Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Signed-off-by: Karol Herbst <kherbst@redhat.com>