nv50/ir: fix TXQ srcMask

src0.x is always read for the LOD, irrespective of which outputs are
read.

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
Cc: mesa-stable@lists.freedesktop.org

src/gallium/drivers/nouveau/codegen/nv50_ir_from_tgsi.cpp

@@ -345,6 +345,8 @@ unsigned int Instruction::srcMask(unsigned int s) const
       }
    }
       return mask;
+   case TGSI_OPCODE_TXQ:
+      return 1;
    case TGSI_OPCODE_XPD:
    {
       unsigned int x = 0;