drm/vmwgfx/vmwgfx_bo: Remove superfluous param description and supply another

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

 drivers/gpu/drm/vmwgfx/vmwgfx_bo.c:142: warning: Excess function parameter 'pin' description in 'vmw_bo_pin_in_vram_or_gmr'
 drivers/gpu/drm/vmwgfx/vmwgfx_bo.c:647: warning: Function parameter or member 'p_base' not described in 'vmw_user_bo_alloc'

Cc: VMware Graphics <linux-graphics-maintainer@vmware.com>
Cc: Roland Scheidegger <sroland@vmware.com>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: dri-devel@lists.freedesktop.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Zack Rusin <zackr@vmware.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210115181313.3431493-28-lee.jones@linaro.org