dt-bindings: media: qcom,x1e80100-camss: Tighten the property regex pattern

There are 4 CSIPHY ports on X1E80100, it'd be preferred to tinker a too
loose the regexp, which covers all these port names.

Signed-off-by: Vladimir Zapolskiy <vladimir.zapolskiy@linaro.org>
Acked-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Bryan O'Donoghue <bod@kernel.org>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>