fs: fix typos of func call in promises.lchmod & lchown

Overview

I fixed 2 typos of function call in fs.promises.

• in lchmod: fschmod to fchmod
• in lchown: fschmod to fchown

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• commit message follows commit guidelines

Affected core subsystem(s)

fs