platform: tegra: nvadsp: Check handle in app init

platform: tegra: nvadsp: Check handle in app init

The NULL pointer check in nvadsp_app_init was removed as a result of
using the single app framework integration. Adding this check back
without which an exception would occur.

Bug 200069519

Change-Id: I8198d1ca5aa3a2f79a3194ac48df0ce70e0753db
Signed-off-by: Ajay Nandakumar <anandakumarm@nvidia.com>
Reviewed-on: http://git-master/r/736727
(cherry picked from commit c7789beded788acfcc4772b3eff0d823baee8b7a)
Reviewed-on: http://git-master/r/744251
Reviewed-by: Automatic_Commit_Validation_User
Reviewed-by: Sachin Nikam <snikam@nvidia.com>