nouveau_gem_ioctl_cpu_prep calls ttm_bo_wait without the bo lock held.
ttm_bo_wait unlocks that lock, and so must be called with it held.

Currently this bug causes libdrm nouveau_bo_busy() to hang the machine.

Signed-off-by: Luca Barbieri <luca at luca-barbieri.com>
Acked-by: NMaarten Maathuis <madman2003@gmail.com>
Signed-off-by: NFrancisco Jerez <currojerez@riseup.net>
Signed-off-by: NBen Skeggs <bskeggs@redhat.com>