video: tegra: nvmap: fix pinning unalloc'd handles

nvmap_pin_ids takes a list of handles to pin from userspace.
Unfortunately, it does not check that the handles are actually
allocated, which will trigger a BUG_ON later in pin_locked().

Bug 1023954

Change-Id: Iba4c53bc0a6c47b7f4f740a93e59b613dc3b95f6
Signed-off-by: Tuomas Tynkkynen <ttynkkynen@nvidia.com>
Reviewed-on: http://git-master/r/131888
Reviewed-by: Mrutyunjay Sawant <msawant@nvidia.com>
Tested-by: Mrutyunjay Sawant <msawant@nvidia.com>