sysfs: fix simple_return.cocci warnings

security/smack/smackfs.c:2251:1-4: WARNING: end returns can be
simpified and declaration on line 2250 can be dropped

 Simplify a trivial if-return sequence.  Possibly combine with a
 preceding function call.

Generated by: scripts/coccinelle/misc/simple_return.cocci

Signed-off-by: Fengguang Wu <fengguang.wu@intel.com>
Acked-by: Serge Hallyn <serge.hallyn@canonical.com>
Acked-by: Casey Schaufler <casey@schaufler-ca.com>