buildroot

fs/jffs2: split commands

Now that we can properly printf a multi-line command, there is no need
to use a single command to gnerate the jffs2 image.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>