docs: usb: fix malformed table

The tables are separated with tabs and spaces mixed together, leading
to malformation. Changed the characters all into spaces to solve this
issue.

Signed-off-by: Hu Haowen <src.res@email.cn>
Link: https://lore.kernel.org/r/20210805040146.121526-1-src.res@email.cn


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