drm: intel_dpio_phy: fix kernel-doc comments at nested struct

The in-lined comments for channel.port doesn't follow the syntax
described at kernel-doc document, causing the following warning:

	$ ./scripts/kernel-doc -none drivers/gpu/drm/i915/intel_dpio_phy.c
	drivers/gpu/drm/i915/intel_dpio_phy.c:154: warning: Function parameter or member 'channel.port' not described in 'bxt_ddi_phy_info'

While the best would be for the Kernel to deduce that from the
context, supporting it is not trivial. So, let's just stick with
the existing syntax.

[Jani: depends on "scripts: kernel-doc: support in-line comments on
nested structs/unions" to actually fix the warning.]

Reported-by: Chris Wilson <chris@chris-wilson.co.uk>
Reported-by: Jani Nikula <jani.nikula@intel.com>
Tested-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/9ba9ac773f4f9e60770bd9169b0e46ac974d858a.1518788761.git.mchehab@s-opensource.com