Add support for compiling for ESX

With contributions from Ryan Haynes <rhaynes@fusionio.com>

Signed-off-by: Jens Axboe <axboe@fb.com>
diff --git a/filesetup.c b/filesetup.c
index 2049fd6..1facccd 100644
--- a/filesetup.c
+++ b/filesetup.c
@@ -390,6 +390,10 @@
 {
 	int ret = 0;
 
+#ifdef CONFIG_ESX
+	return 0;
+#endif
+
 	if (len == -1ULL)
 		len = f->io_size;
 	if (off == -1ULL)