וַיְדַבֵּר֙ שַׂ֣ר הַמַּשְׁקִ֔ים אֶת־פַּרְעֹ֖ה לֵאמֹ֑ר אֶת־חֲטָאַ֕י אֲנִ֖י מַזְכִּ֥יר הַיּֽוֹם׃
האָט דער אױבערטראַנקמײַסטער גערעדט צו פַּרעהן, אַזױ צו זאָגן: מײַנע זינד מוז איך הײַנט דערמאָנען.
Chizkuni
את חטאי, “my sins;” the plural mode the cupbearer chose here was to admit his sins against Pharaoh as well as his sin in not fulfilling his promise to Joseph through his forgetfulness.
Sforno
את חטאי אני מזכיר, not because I want to complain that you, O King, had placed me in prison, for it was my sin that caused this
Or HaChaim
וידבר שר המשקים את פרעה, The chief butler said to Pharaoh saying, etc. The reason the Torah had to add the word לאמור as well as the word את פרעה instead of אל פרעה, maybe that the chief butler did not address the King personally but his advisers. He asked the king's advisers to relay his words to the king. This is the reason that his entire speech is in the third person.