configure: fix mis-generation of compat.h for no __kernel_rwf_t

Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/configure b/configure
index 95cf8cd..a52644f 100755
--- a/configure
+++ b/configure
@@ -270,7 +270,7 @@
 EOF
 
 if test "$__kernel_rwf_t" != "yes"; then
-cat > $compat_h << EOF
+cat >> $compat_h << EOF
 typedef int __kernel_rwf_t;
 
 EOF