i965/fs: Report the right value in fs_inst::regs_read() for PIXEL_X/Y
i965/fs: Report the right value in fs_inst::regs_read() for PIXEL_X/Y

Reviewed-by: Iago Toral Quiroga <a847aabaac44184372f6b1cd1a59aa254daaeb0b@igalia.com>
Reviewed-by: Topi Pohjolainen <749697f19798b7f640b17221fd283b903825f071@intel.com>
Acked-by: Francisco Jerez <5906ff32bdd9fd8db196f6ba5ad3afd6f9257ea5@riseup.net>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler