drm/connector: fix minor typos in comments

Some of these comments are part of the Linux GPU Driver Developer's
Guide.
Fix some minor typo in the comments and remove a repeated 'the'.

Signed-off-by: Antonio Borneo <antonio.borneo@st.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20200626204252.44565-1-antonio.borneo@st.com