usb/storage: remove Filler member from struct bulk_cs_wrap

As Alan Stern pointed out this member has nothing to do with the Command
Status Wrapper (CSW) as specified by the Universal Serial Bus Mass
Storage Class Bulk-Only Transport rev 1.0. It defines the structure
without the additional 18 filler bytes and defines the total size of the
struct to exactly 13 bytes. Larger responses should be dropped. All
in-tree users use a defines instead of sizeof() of this struct as far I
can tell.

Cc: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>