drm/dp: Fix documentation of DP tunnel functions

Fix the documentation issues below, also reported by 'make htmldocs':

drivers/gpu/drm/display/drm_dp_tunnel.c:447: warning: Function parameter or struct member 'tunnel' not described in 'drm_dp_tunnel_put'
drivers/gpu/drm/display/drm_dp_tunnel.c:447: warning: Function parameter or struct member 'tracker' not described in 'drm_dp_tunnel_put'
drivers/gpu/drm/display/drm_dp_tunnel.c:1185: warning: expecting prototype for drm_dp_tunnel_atomic_get_allocated_bw(). Prototype was for drm_dp_tunnel_get_allocated_bw() instead
drivers/gpu/drm/display/drm_dp_tunnel.c:1903: warning: Function parameter or struct member 'max_group_count' not described in 'drm_dp_tunnel_mgr_create'

Fixes: 295654f7 ("drm/dp: Add support for DP tunneling")
Reported-by: kernel test robot <lkp@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240228164636.1540903-1-imre.deak@intel.com