Input: vmmouse - demote obvious abuse of kernel-doc header

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

 drivers/input/mouse/vmmouse.c:99: warning: Function parameter or member 'cmd' not described in 'VMMOUSE_CMD'
 drivers/input/mouse/vmmouse.c:99: warning: Function parameter or member 'in1' not described in 'VMMOUSE_CMD'
 drivers/input/mouse/vmmouse.c:99: warning: Function parameter or member 'out1' not described in 'VMMOUSE_CMD'
 drivers/input/mouse/vmmouse.c:99: warning: Function parameter or member 'out2' not described in 'VMMOUSE_CMD'
 drivers/input/mouse/vmmouse.c:99: warning: Function parameter or member 'out3' not described in 'VMMOUSE_CMD'
 drivers/input/mouse/vmmouse.c:99: warning: Function parameter or member 'out4' not described in 'VMMOUSE_CMD'

Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20201112110204.2083435-16-lee.jones@linaro.org
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>