net: fddi: skfp: smt: Place definition of 'smt_pdef' under same stipulations as its use

The variable 'smt_pdef' is only used if LITTLE_ENDIAN is set, so only
define it if this is the case.

Fixes the following W=1 kernel build warning(s):

 drivers/net/fddi/skfp/smt.c:1572:3: warning: ‘smt_pdef’ defined but not used [-Wunused-const-variable=]

Cc: "David S. Miller" <davem@davemloft.net>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: netdev@vger.kernel.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>