usb: correct kernel-doc inconsistency

usb: correct kernel-doc inconsistency

Silence documentation  build warning by correcting  kernel-doc comment
for sub_validate_langid function.

./drivers/usb/gadget/usbstring.c:77: warning: Function parameter or member 'langid' not described in 'usb_validate_langid'
./drivers/usb/gadget/usbstring.c:77: warning: Excess function parameter 'lang' description in 'usb_validate_langid'

Signed-off-by: Colton Lewis <colton.w.lewis@protonmail.com>
Link: https://lore.kernel.org/r/20200707045207.235540-1-colton.w.lewis@protonmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>