Rashi on Genesis
נמצא חן LET US FIND FAVOUR — [IN THE EYES OF MY LORD] in that you should do for us as you have said.
Or HaChaim on Genesis
והיינו עבדים לפרעה, "and we shall remain slaves to Pharaoh." They were careful to describe themselves as Pharaoh's slaves, not as Joseph's.
Tur HaArokh
החייתנו...והיינו עבדים לפרעה, “you have saved our lives, and we have becoming willing slaves of Pharaoh.” The emphasis on the unnecessary word לפרעה was a blunt hint to Joseph that whereas they were willing to become Pharaoh’s slaves, they would not have been willing to become Joseph’s slaves.