vm_mmap should be called with page offset in bytes

We now call vm_mmap instead of do_mmap_pgoff. vm_mmap takes a page offset in
bytes, not page numbers.

Signed-off-by: Mike McClurg <mike.mcclurg@citrix.com>
Remove redundant mmap_sem locks, replace with mutex

When the interface to do_mmap_pgoff changed, we were forced to call vm_mmap
instead. vm_mmap takes a lock on the mmap_sem, so taking those locks in ring.c
causes deadlock. We remove those semaphore locks now, and replace them with
mutexes.

Signed-off-by: Mike McClurg <mike.mcclurg@citrix.com>
Merge pull request #3 from mcclurmc/linux-3.5-xenorg

Fix for Linux 3.5 kernel changes -- unblocks Ubuntu Quantal