Camera: Fix doc parameter description typo

The 'CaptureRequest.Builder.setPhysicalCameraKey'
return value and parameter description contain
a typo that must be corrected.

Bug: 140915387
Test: make -j42 docs,
manual check of generated docs

Change-Id: I6f17df1917a7381c4119b9fcff3c5b8b18c5faa6