SHMEM: silence warning

Refs trac:3763

This commit was SVN r30077.

The following Trac tickets were found above:
  Ticket 3763 --> https://svn.open-mpi.org/trac/ompi/ticket/3763

oshmem/mca/memheap/base/memheap_base_mkey.c

@@ -67,6 +67,8 @@ struct oob_comm memheap_oob;
 
 static int send_buffer(int pe, opal_buffer_t *msg);
 
+int oshmem_mkey_recv_cb(void);
+
 /* pickup list of rkeys and remote va */
 static int memheap_oob_get_mkeys(int pe,
                                  uint32_t va_seg_num,
@@ -412,7 +414,7 @@ static inline int my_MPI_Test(ompi_request_t ** rptr,
     return OMPI_SUCCESS;
 }
 
-int oshmem_mkey_recv_cb(void)
+static int oshmem_mkey_recv_cb(void)
 {
     MPI_Status status;
     int flag;