drm/vmwgfx/vmwgfx_drv: Fix some kernel-doc misdemeanours

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

 drivers/gpu/drm/vmwgfx/vmwgfx_drv.c:164: warning: Function parameter or member 'ioctl' not described in 'VMW_IOCTL_DEF'
 drivers/gpu/drm/vmwgfx/vmwgfx_drv.c:164: warning: Function parameter or member 'func' not described in 'VMW_IOCTL_DEF'
 drivers/gpu/drm/vmwgfx/vmwgfx_drv.c:164: warning: Function parameter or member 'flags' not described in 'VMW_IOCTL_DEF'
 drivers/gpu/drm/vmwgfx/vmwgfx_drv.c:170: warning: cannot understand function prototype: 'const struct drm_ioctl_desc vmw_ioctls[] = '
 drivers/gpu/drm/vmwgfx/vmwgfx_drv.c:542: warning: Function parameter or member 'dev_priv' not described in 'vmw_get_initial_size'
 drivers/gpu/drm/vmwgfx/vmwgfx_drv.c:611: warning: Function parameter or member 'dev_priv' not described in 'vmw_dma_masks'
 drivers/gpu/drm/vmwgfx/vmwgfx_drv.c:611: warning: Excess function parameter 'dev' description in 'vmw_dma_masks'

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/20210115181313.3431493-9-lee.jones@linaro.org