arm64: dts: qcom: sc8280xp-x13s: mark s11b regulator as always-on

The s11b supply is used by the wlan module (as well as some of the
pmics) which are not yet fully described in the devicetree.

Mark the regulator as always-on for now.

Fixes: 123b30a7

 ("arm64: dts: qcom: sc8280xp-x13s: enable WiFi controller")
Cc: stable@vger.kernel.org	# 6.2
Signed-off-by: Johan Hovold <johan+linaro@kernel.org>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20230322113318.17908-2-johan+linaro@kernel.org