drm/amdgpu: Fix missing parameter descriptions in ih_v7_0.c

Rectifies kdoc warnings related to the 'ih' parameter in the
'ih_v7_0_get_wptr', 'ih_v7_0_irq_rearm', and 'ih_v7_0_set_rptr'
functions within the 'ih_v7_0.c' file.

Fixes the below with gcc W=1:
drivers/gpu/drm/amd/amdgpu/ih_v7_0.c:392: warning: Function parameter or member 'ih' not described in 'ih_v7_0_get_wptr'
drivers/gpu/drm/amd/amdgpu/ih_v7_0.c:432: warning: Function parameter or member 'ih' not described in 'ih_v7_0_irq_rearm'
drivers/gpu/drm/amd/amdgpu/ih_v7_0.c:458: warning: Function parameter or member 'ih' not described in 'ih_v7_0_set_rptr'

Fixes: 12443fc5

 ("drm/amdgpu: Add ih v7_0 ip block support")
Cc: Likun Gao <Likun.Gao@amd.com>
Cc: Hawking Zhang <Hawking.Zhang@amd.com>
Cc: Christian König <christian.koenig@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Srinivasan Shanmugam <srinivasan.shanmugam@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>