regulator: qcom_smd: Add s1 sub-node to mp5496 regulator

Adding s1 sub-node entry to mp5496 regulator node.

Reviewed-by: Rob Herring <[e-mail]>
Signed-off-by: Devi Priya <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Mark Brown <[e-mail]>

Documentation/devicetree/bindings/regulator/qcom,smd-rpm-regulator.yaml

···
   Each sub-node is identified using the node's name, with valid values listed
   for each of the pmics below.
 
-  For mp5496, s2
+  For mp5496, s1, s2
 
   For pm2250, s1, s2, s3, s4, l1, l2, l3, l4, l5, l6, l7, l8, l9, l10, l11,
   l12, l13, l14, l15, l16, l17, l18, l19, l20, l21, l22