drm/i915/hmdi: Rename set_infoframe() to write_infoframe()

set_frame() wraps the write_frame() vfunc. Be consistent and name the
wrapping function like the vfunc being called.

It's doubly confusing as we also have a set_infoframes() vfunc and
set_infoframe() doesn't wrap it.

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>