drm/amd/display: fix memory leak when using debugfs_lookup()

When calling debugfs_lookup() the result must have dput() called on it,
otherwise the memory will leak over time.  Fix this up by properly
calling dput().

Cc: Harry Wentland <harry.wentland@amd.com>
Cc: Leo Li <sunpeng.li@amd.com>
Cc: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: "Christian König" <christian.koenig@amd.com>
Cc: "Pan, Xinhui" <Xinhui.Pan@amd.com>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Wayne Lin <Wayne.Lin@amd.com>
Cc: hersen wu <hersenxs.wu@amd.com>
Cc: Wenjing Liu <wenjing.liu@amd.com>
Cc: Patrik Jakobsson <patrik.r.jakobsson@gmail.com>
Cc: Thelford Williams <tdwilliamsiv@gmail.com>
Cc: Fangzhi Zuo <Jerry.Zuo@amd.com>
Cc: Yongzhi Liu <lyz_cs@pku.edu.cn>
Cc: Mikita Lipski <mikita.lipski@amd.com>
Cc: Jiapeng Chong <jiapeng.chong@linux.alibaba.com>
Cc: Bhanuprakash Modem <bhanuprakash.modem@intel.com>
Cc: Sean Paul <seanpaul@chromium.org>
Cc: amd-gfx@lists.freedesktop.org
Cc: dri-devel@lists.freedesktop.org
Cc: stable@vger.kernel.org
Reviewed-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>