hte: tegra: Fix missing error code in tegra_hte_test_probe()

The value of 'ret' is zero when of_hte_req_count() fails to get number
of entitties to timestamp. And returning success(zero) on this failure
path is incorrect.

Fixes: 9a75a7cd ("hte: Add Tegra HTE test driver")
Signed-off-by: Harshit Mogalapalli <harshit.m.mogalapalli@oracle.com>
Reviewed-by: Dipen Patel <dipenp@nvidia.com>
Signed-off-by: Dipen Patel <dipenp@nvidia.com>