Remove extra unlock in dm9000 driver

[Lwazi Dube <lwazeh%gmail.com@localhost>]

diff --git a/sys/dev/ic/dm9000.c b/sys/dev/ic/dm9000.c
index 316ba0c44286..b268946bfc0c 100644
--- a/sys/dev/ic/dm9000.c
+++ b/sys/dev/ic/dm9000.c
@@ -442,7 +442,6 @@ dme_set_rcvfilt(struct dme_softc *sc)
              * range is big enough to require all bits set.)
              */
             ec->ec_flags |= ETHER_F_ALLMULTI;
-            ETHER_UNLOCK(ec);
             memset(mchash, 0xff, sizeof(mchash)); /* necessary? */
             /* accept all mulicast frame */
             rcr |= DM9000_RCR_ALL;