tslib: use FILESEXTRAPATHS_prepend for correct assignment
tslib: use FILESEXTRAPATHS_prepend for correct assignment

Signed-off-by: Jonathan Liu <44960b6aa03eb2fb89c62409a43f0b56d13ff84f@gmail.com>

O-Computers/meta-sunxi,ebutera/meta-sunxi,jlucius/meta-sunxi,linux-sunxi/meta-sunxi,geomatsi/meta-sunxi,jlucius/meta-sunxi,linux-sunxi/meta-sunxi,twoerner/meta-sunxi,rofehr/meta-sunxi,rofehr/meta-sunxi,net147/meta-sunxi,rofehr/meta-sunxi,linux-sunxi/meta-sunxi,jlucius/meta-sunxi,geomatsi/meta-sunxi,O-Computers/meta-sunxi,soderstrom-rikard/meta-sunxi,ebutera/meta-sunxi,net147/meta-sunxi,twoerner/meta-sunxi,O-Computers/meta-sunxi,soderstrom-rikard/meta-sunxi