soc: qcom: rmtfs: fix error handling reading qcom,vmid

of_property_count_u32_elems returns a negative integer when an error
happens , but since the value was assigned to an unsigned integer, the
check never worked correctly. Also print the correct variable in the
error print, ret isn't used here.

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-v1-1-6a7206081602@z3ntu.xyz