filesystems: also chown symlinks

Currently, the symlinks in the generated filesystems will have the
UID of the user running the build, because 'chown' does not change
the ownership of symlinks, by default.

Although the implications are limited, some may not want that UID
to leak in the generated filesystems.

So, use 'chown -h' so even symlinks get properly chowned.

Reported-by: Angelo Dureghello <angelo@barix.com>
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Thomas De Schampheleire <patrickdepinguin@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>