soc: qcom: rmtfs: handle optional qcom,vmid correctly

Older platforms don't have qcom,vmid set, handle -EINVAL return value
correctly. And since num_vmids is passed to of_property_read_u32_array
later we should make sure it has a sane value before continuing.

Fixes: e656cd0b

 ("soc: qcom: rmtfs: Optionally map RMTFS to more VMs")
Signed-off-by: Luca Weiss <luca@z3ntu.xyz>
Reviewed-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20230305-rmtfs-vmid-fix-v1-2-6a7206081602@z3ntu.xyz