Update for RDMA io engine's compatibility

Since the RDMA engine is not able to be successfully compiled, this
patch accommodates it to the upstream version of fio.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/configure b/configure
index 98af5ff..c00a3a4 100755
--- a/configure
+++ b/configure
@@ -1127,7 +1127,7 @@
 if test "$sfaa" = "yes" ; then
   output_sym "CONFIG_SFAA"
 fi
-if test "$libverbs" = "yes" -a "rdmacm" = "yes" ; then
+if test "$libverbs" = "yes" -a "$rdmacm" = "yes" ; then
   output_sym "CONFIG_RDMA"
 fi
 if test "$clock_gettime" = "yes" ; then