dmaengine: ioatdma: fix coccinelle warning

Simplifying the end return. This existed in the original code but was
flagged when refactoring of the code made it appear it's new.

coccinelle warnings: (new ones prefixed by >>)

>> drivers/dma/ioat/init.c:1018:1-3: WARNING: end returns can be simpified

Signed-off-by: Dave Jiang <dave.jiang@intel.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>