Fix return value of selinux_android_restorecon.

Change I4a380caab7f8481c33eb64fcdb16b6cabe918ebd unified
the init and libselinux restorecon code but introduced a bug
by changing the return value of selinux_android_restorecon
on errors from -1 (as in libselinux) to -errno (as in the init
built-in command).  Change it back as there are various callers
assuming the libselinux behavior and init does not actually rely
on the -errno behavior in the utils code and handles it correctly
in the built-in command functions themselves.

Change-Id: I6ed5b644820eb07c061d8a2a116511aeb7401df4
Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>