[][Fix spi dma unmap]

[Description]
Change where dma_unmap_single is called,use dma_unmap_single before memcpy to ensure that CPU can get the latest and correct data

[Release-log]
N/A

Change-Id: Ie3470c050432452d3a18e819c696b079ebb51d0c
Reviewed-on: https://gerrit.mediatek.inc/c/openwrt/feeds/mtk_openwrt_feeds/+/7088823
1 file changed