Remove unused local `us', which broke the build.  Also nuke an unneeded
cast.

Repairs commit 191648d0 ("usb: storage: Convert US_DEBUGP to
usb_stor_dbg").

Cc: Joe Perches <joe@perches.com>
Acked-by: David Rientjes <rientjes@google.com>
Cc: Greg KH <greg@kroah.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>