fp5280g2: Fix the file extra path error

When built the related SDK on fp5280g2, since the wrong FILESEXTRAPATHS
were defined and the build failed.

Tested: built successfully on fp5280g2 using related SDK.

(From meta-inspur rev: 68b943d9f121e11b01e9a60a595930d50b16d13e)

Signed-off-by: George Liu <liuxiwei@inspur.com>
Change-Id: I6e1edd74883e8d7910facd15f800aa954bd402a7
Signed-off-by: Andrew Geissler <geissonator@yahoo.com>