drm/amd/amdgpu/amdgpu_ring: Fix a bunch of function misdocumentation

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

 drivers/gpu/drm/amd/amdgpu/amdgpu_ring.c:63: warning: Excess function parameter 'adev' description in 'amdgpu_ring_alloc'
 drivers/gpu/drm/amd/amdgpu/amdgpu_ring.c:122: warning: Excess function parameter 'adev' description in 'amdgpu_ring_commit'
 drivers/gpu/drm/amd/amdgpu/amdgpu_ring.c:167: warning: Function parameter or member 'max_dw' not described in 'amdgpu_ring_init'
 drivers/gpu/drm/amd/amdgpu/amdgpu_ring.c:167: warning: Function parameter or member 'irq_src' not described in 'amdgpu_ring_init'
 drivers/gpu/drm/amd/amdgpu/amdgpu_ring.c:167: warning: Function parameter or member 'irq_type' not described in 'amdgpu_ring_init'
 drivers/gpu/drm/amd/amdgpu/amdgpu_ring.c:167: warning: Function parameter or member 'hw_prio' not described in 'amdgpu_ring_init'
 drivers/gpu/drm/amd/amdgpu/amdgpu_ring.c:167: warning: Excess function parameter 'max_ndw' description in 'amdgpu_ring_init'
 drivers/gpu/drm/amd/amdgpu/amdgpu_ring.c:167: warning: Excess function parameter 'nop' description in 'amdgpu_ring_init'
 drivers/gpu/drm/amd/amdgpu/amdgpu_ring.c:285: warning: Excess function parameter 'adev' description in 'amdgpu_ring_fini'
 drivers/gpu/drm/amd/amdgpu/amdgpu_ring.c:325: warning: Function parameter or member 'ring' not described in 'amdgpu_ring_emit_reg_write_reg_wait_helper'
 drivers/gpu/drm/amd/amdgpu/amdgpu_ring.c:325: warning: Excess function parameter 'adev' description in 'amdgpu_ring_emit_reg_write_reg_wait_helper'

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: Sumit Semwal <sumit.semwal@linaro.org>
Cc: amd-gfx@lists.freedesktop.org
Cc: dri-devel@lists.freedesktop.org
Cc: linux-media@vger.kernel.org
Cc: linaro-mm-sig@lists.linaro.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>