Fixes gcc '-Wunused-but-set-variable' warning:

drivers/usb/gadget/legacy/acm_ms.c: In function acm_ms_do_config:
drivers/usb/gadget/legacy/acm_ms.c:108:19: warning: variable opts set but not used [-Wunused-but-set-variable]

It is not used since commit f78bbcae ("usb: f_mass_storage:
test whether thread is running before starting another")
Reported-by: NHulk Robot <hulkci@huawei.com>
Signed-off-by: Nzhengbin <zhengbin13@huawei.com>
Link: https://lore.kernel.org/r/1570610434-68293-2-git-send-email-zhengbin13@huawei.comSigned-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>