Oops! Remove unneeded memory barrier.

This commit was SVN r24096.

ompi/mca/btl/sm/btl_sm.h

@@ -342,7 +342,6 @@ static inline int sm_fifo_write(void *value, sm_fifo_t *fifo)
     q[fifo->head] = value;
     opal_atomic_wmb();
     fifo->head = (fifo->head + 1) & fifo->mask;
-    opal_atomic_wmb(); 
     return OMPI_SUCCESS;
 }