dropbear: Fix postfuncs overrides
dropbear: Fix postfuncs overrides

Using append overrides must in such cases be preceeded by a space.

Signed-off-by: Esben Haabendal <esben.haabendal@prevas.dk>

(cherry picked from commit 7ffbcbe74757dd097d934f2a2b25fd31cf2ee727)

oe-lite-rpi/base,jacobbarsoe/rpi-base,oe-lite-rpi/base,jacobbarsoe/rpi-base