DMAEngine: sirf: lock the shared registers access in sirfsoc_dma_terminate_all

Just like Russell pointed out in "DMAEngine: sirf: add DMA
pause/resume support" at
http://www.spinics.net/lists/arm-kernel/msg212496.html
here I find sirfsoc_dma_terminate_all() has same problem,
so move the locking to the front of registers access.

Signed-off-by: Barry Song <Baohua.Song@csr.com>
Cc: Russell King <linux@arm.linux.org.uk>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>