dt-bindings: mfd: qcom,spmi-pmic: Rename extcon node name

extcon is a Linux-specific name and shouldn't be a part of the dts. Make
it be called usb-detect@ instead.

Signed-off-by: Luca Weiss <luca@z3ntu.xyz>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Lee Jones <lee@kernel.org>
Link: https://lore.kernel.org/r/20221031175717.942237-1-luca@z3ntu.xyz