Finally it works 🙂 But still not perfect.
Thanks for noltari find the problem. Just change spi speed line in dts, then it works.

Here is the patch and new spi-rt2880.c(rewrite by noltari)
vocore_spi_sd_#1
spi-rt2880

Here is the screen capture.

PS: here is the patch of VoCoreopenwrt-vocore patch
1. change ap to VoCore to avoid ap name conflict with other openwrt device.
2. change default ip to 192.168.61.1 to avoid ap+sta mode ip conflict.
3. change shadow file, so there is default password “vocore”
4. change dts flash partition to fit 16MB flash.(keep the line if you are using 8MB version vocore)

Here is the link of compiled firmware: vocore.16m.microsd.bin