USB: ehci: Minor constant fix for SCHEDULE_SLOP.

Change the constant SCHEDULE_SLOP to be 80 microframes, instead of 10
frames.  It was always multiplied by 8 to convert frames to microframes.
SCHEDULE_SLOP is only used in ehci-sched.c.

Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Cc: David Brownell <dbrownell@users.sourceforge.net>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>