gpu: nvgpu: use correct API to check valid syncpt

gpu: nvgpu: use correct API to check valid syncpt

Below check assumes that available syncpt range
starts from 0
id >= nvhost_syncpt_nb_pts_ext()

Instead of using this API, use nvhost_syncpt_is_valid_pt_ext()
which validates the syncpt id against both upper and lower
boundaries

Bug 1611482

Change-Id: I7c4465a2bc84b63fefaa17c64f02582885924c5e
Signed-off-by: Deepak Nibade <dnibade@nvidia.com>
Reviewed-on: http://git-master/r/711211
Reviewed-by: Automatic_Commit_Validation_User
Reviewed-by: Terje Bergstrom <tbergstrom@nvidia.com>
Reviewed-by: Arto Merilainen <amerilainen@nvidia.com>