dmaengine: tegra-apb: Don't save/restore IRQ flags in interrupt handler

The interrupt is already disabled while interrupt handler is running, and
thus, there is no need to save/restore the IRQ flags within the spinlock.

Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Link: https://lore.kernel.org/r/20200319212321.3297-1-digetx@gmail.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>