i965/vec4: Initialize nir_inputs with src_reg().
i965/vec4: Initialize nir_inputs with src_reg().

nir_locals, nir_ssa_values, and nir_system_values are all dst_reg (not
that that makes a whole lot of sense to me), and only nir_inputs is a
src_reg.

Reviewed-by: Francisco Jerez <5906ff32bdd9fd8db196f6ba5ad3afd6f9257ea5@riseup.net>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler