fs: Bail out on errors in fakeroot script

Currently, the generated fakeroot script has no error checking causing
make to continue building even if some of the fakeroot script commands
have failed. This can cause e.g. using an invalid device tables to go
unnoticed.

So add a "set -e" to the start of the fakeroot script so it will exit
with a failure code as soon as one of the script commands fails.

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