dt-bindings: mux: mux.h: drop a duplicated word

Drop the repeated word "the" in a comment.

Cc: Peter Rosin <peda@axentia.se>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: devicetree@vger.kernel.org
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Link: https://lore.kernel.org/r/20200719002816.20263-1-rdunlap@infradead.org
Signed-off-by: Rob Herring <robh@kernel.org>