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

This patch moves the HcInterrupt register write to clear the
pending interrupt to after the isr work is done, doing this removes
glitches in the irq line.

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