drm/vmwgfx: (Re)bind shaders to MOBs with the correct offset

This codepath is mostly hit when rebinding after a backup buffer swapout. It's
amazing that this error hasn't been more obvious but probably the shaders are
not reread from guest memory that often..

Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Reviewed-by: Jakob Bornecrantz <jakob@vmware.com>
Reviewed-by: Sinclair Yeh <syeh@vmware.com>