Revert "USB: isp1760-hcd: move imask clear after pending work is done"

This reverts commit 58085446.

To quote Richard:
	I don't think this should be mainlined. It was a
	misunderstanding on my part.  If you see all the other hdc
	drivers in the same location, they all do the same thing (i.e.
	clear the interrupt status first, then do the work) that
	"glitch" I think I saw was actually two back-to-back
	interrupts.

	Sebastian (the original author of isp1760) explained it to me a
	few days after my submission.

	sorry for the confusion

Cc: Richard Retanubun <RichardRetanubun@ruggedcom.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>