i965/blorp: Stop doing f2i(i2f(sample_id))
i965/blorp: Stop doing f2i(i2f(sample_id))

NIR gets kind of awkward when you have a 3-component vector with two floats
and one int.  This led to us accidentally going through float for the
sample index.  It doesn't hurt anything but it also isn't needed.

Reviewed-by: Topi Pohjolainen <749697f19798b7f640b17221fd283b903825f071@intel.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler