dmaengine: ioat: Make two symbols static

dmaengine: ioat: Make two symbols static

This eliminates the following sparse warning:

drivers/dma/ioat/dma.c:29:5: warning: symbol 'completion_timeout' was
not declared. Should it be static?
drivers/dma/ioat/dma.c:33:5: warning: symbol 'idle_timeout' was not
declared. Should it be static?

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Jason Yan <yanaijie@huawei.com>
Acked-by: Dave Jiang <dave.jiang@intel.com>
Link: https://lore.kernel.org/r/20200912072158.602585-1-yanaijie@huawei.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>