usb: mtu3: mtu3_core: Demote obvious misuse of kerneldoc to standard comment block

usb: mtu3: mtu3_core: Demote obvious misuse of kerneldoc to standard comment block

No attempt has been made to document the function.

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

 drivers/usb/mtu3/mtu3_core.c:805: warning: Function parameter or member 'mtu' not described in 'mtu3_set_dma_mask'

Cc: Chunfeng Yun <chunfeng.yun@mediatek.com>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-mediatek@lists.infradead.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20200702144625.2533530-26-lee.jones@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>