dma-mapping: fix return type of dma_set_max_seg_size()

The function dma_set_max_seg_size() can return either 0 on success or
-EIO on error. Change its return type from unsigned int to int to
capture this.

Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Christoph Hellwig <hch@lst.de>