drm/amd/amdgpu/jpeg_v2_0: Add some missing kernel-doc descriptions

Fixes the following W=1 kernel build warning(s):

 drivers/gpu/drm/amd/amdgpu/jpeg_v2_0.c:498: warning: Function parameter or member 'addr' not described in 'jpeg_v2_0_dec_ring_emit_fence'
 drivers/gpu/drm/amd/amdgpu/jpeg_v2_0.c:498: warning: Function parameter or member 'seq' not described in 'jpeg_v2_0_dec_ring_emit_fence'
 drivers/gpu/drm/amd/amdgpu/jpeg_v2_0.c:498: warning: Function parameter or member 'flags' not described in 'jpeg_v2_0_dec_ring_emit_fence'
 drivers/gpu/drm/amd/amdgpu/jpeg_v2_0.c:498: warning: Excess function parameter 'fence' description in 'jpeg_v2_0_dec_ring_emit_fence'
 drivers/gpu/drm/amd/amdgpu/jpeg_v2_0.c:549: warning: Function parameter or member 'job' not described in 'jpeg_v2_0_dec_ring_emit_ib'
 drivers/gpu/drm/amd/amdgpu/jpeg_v2_0.c:549: warning: Function parameter or member 'flags' not described in 'jpeg_v2_0_dec_ring_emit_ib'

Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: "Christian König" <christian.koenig@amd.com>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: amd-gfx@lists.freedesktop.org
Cc: dri-devel@lists.freedesktop.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>