docs: ABI: fixed req_number desc in UAC1

Fixed wording of the req_number description in UAC1 docs.

Signed-off-by: Pavel Hofman <pavel.hofman@ivitera.com>
Link: https://lore.kernel.org/r/20211225130929.205629-2-pavel.hofman@ivitera.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>