video: tegra: host: Fix crash if allocation fails

nvhost_module_remove_client assumes that a client structure
to be freed exists in the linked list. However, if an allocation fails
in nvhost_module_add_client, no client structure is allocated, and
during cleanup, nvhost_module_remove_client would then attempt
to free an invalid pointer.

Bug 1034729

Change-Id: Ie1a641071b86f8246951e9be824a6003f14b04b6
Signed-off-by: Tuomas Tynkkynen <ttynkkynen@nvidia.com>
Reviewed-on: http://git-master/r/124096
Reviewed-by: Automatic_Commit_Validation_User
GVS: Gerrit_Virtual_Submit
Reviewed-by: Terje Bergstrom <tbergstrom@nvidia.com>
Reviewed-by: Juha Tukkinen <jtukkinen@nvidia.com>