dt-bindings: soc: fsl: cpm_qe: cpm1-scc-qmc: Fix example property name

The given example mentions the 'fsl,mode' property whereas the
correct property name, the one described, is 'fsl,operational-mode'.

Fix the example to use the correct property name.

Fixes: a9b12132

 ("dt-bindings: soc: fsl: cpm_qe: Add QMC controller")
Signed-off-by: Herve Codina <herve.codina@bootlin.com>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20231011061437.64213-7-herve.codina@bootlin.com
Signed-off-by: Rob Herring <robh@kernel.org>