i915: fix build warning in intel_dp_get_link_status()

There is a build warning using gcc-11 showing a mis-match in the .h and .c
definitions of intel_dp_get_link_status():
  CC [M]  drivers/gpu/drm/i915/display/intel_dp.o
drivers/gpu/drm/i915/display/intel_dp.c:4139:56: warning: argument 2 of type ‘u8[6]’ {aka ‘unsigned char[6]’} with mismatched bound [-Warray-parameter=]
 4139 | intel_dp_get_link_status(struct intel_dp *intel_dp, u8 link_status[DP_LINK_STATUS_SIZE])
      |                                                     ~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from drivers/gpu/drm/i915/display/intel_dp.c:51:
drivers/gpu/drm/i915/display/intel_dp.h:105:57: note: previously declared as ‘u8 *’ {aka ‘unsigned char *’}
  105 | intel_dp_get_link_status(struct intel_dp *intel_dp, u8 *link_status);
      |                                                     ~~~~^~~~~~~~~~~

This was fixed accidentally commit b30edfd8 ("drm/i915: Switch to LTTPR
non-transparent mode link training") by getting rid of the function entirely,
but that is not a viable backport for a stable kernel, so just fix up the
function definition to remove the build warning entirely.  There is no
functional change for this, and it fixes up one of the last 'make allmodconfig'
build warnings when using gcc-11 on this kernel tree.

Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>