dmaengine: plx_dma: Move spin_lock_bh() to spin_lock()

It is unnecessary to call spin_lock_bh() if you are already in a tasklet.

Signed-off-by: Yunbo Yu <yuyunbo519@gmail.com>
Reviewed-by: Logan Gunthorpe <logang@deltatee.com>
Link: https://lore.kernel.org/r/20220418142021.1241558-1-yuyunbo519@gmail.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>