usb: storage: Limit transfer size to 120 kiB

Due to constant influx of more and more weird and broken USB sticks,
do as Linux does in commit 779b457f66e10de3471479373463b27fd308dc85

    usb: storage: scsiglue: further describe our 240 sector limit

    Just so we have some sort of documentation as to why
    we limit our Mass Storage transfers to 240 sectors,
    let's update the comment to make clearer that
    devices were found that would choke with larger
    transfers.

    While at that, also make sure to clarify that other
    operating systems have similar, albeit different,
    limits on mass storage transfers.

And reduce the maximum transfer length of USB storage to 120 kiB.

Signed-off-by: Marek Vasut <marek.vasut+renesas@gmail.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Cc: Bin Meng <bmeng.cn@gmail.com>
Cc: Simon Glass <sjg@chromium.org>