When we hold for the lock for swapping out the shmem pages for the
physically contiguous pages, we have to call the unlocked version of
get_pages!

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=101934
Fixes: 35d23516946e ("drm/i915: Make i915_gem_object_phys_attach() use obj->mm.lock more appropriately")
Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20170726181602.23527-2-chris@chris-wilson.co.ukReviewed-by: NMatthew Auld <matthew.auld@intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>