USB: ehci: remove obsolete workaround for bogus IRQs

It was pointed out that we found and fixed the cause of the "bogus"
fatal IRQ reports some time ago ... this patch removes the code
which was working around that bug ("status" got clobbered), and a
comment which needlessly confused folk reading this code.

This also includes a minor cleanup to the code which fixed that bug.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>