Fix thinko in types_darwin.go

Ensure all.bash tests compilation on both Darwin and Linux.

Fixes #125.

all.bash

@@ -6,6 +6,13 @@ for d in fuse zipfs unionfs fuse/test
 do
     (
         cd $d
+
+        # Make sure it compiles on all platforms.
+        for GOOS in darwin linux ; do
+          export GOOS
+          go test -c -i github.com/hanwen/go-fuse/$d
+        done
+
         echo "go test github.com/hanwen/go-fuse/$d"
         go test github.com/hanwen/go-fuse/$d
         echo "go test -race github.com/hanwen/go-fuse/$d"

fuse/types_darwin.go

@@ -148,6 +148,6 @@ func (s *StatfsOut) FromStatfsT(statfs *syscall.Statfs_t) {
 	s.Bavail = statfs.Bavail
 	s.Files = statfs.Files
 	s.Ffree = statfs.Ffree
-	s.Bsize = uint32(s.Iosize) // Iosize translates to Bsize: the optimal transfer size.
+	s.Bsize = uint32(statfs.Iosize) // Iosize translates to Bsize: the optimal transfer size.
 	s.Frsize = s.Bsize              // Bsize translates to Frsize: the minimum transfer size.
 }