dt-bindings: timer: Update maintainers for st,stm32-timer

Benjamin has left the company, add Fabrice and myself as maintainers.

Signed-off-by: Patrice Chotard <patrice.chotard@foss.st.com>
Link: https://lore.kernel.org/r/20211110150144.18272-2-patrice.chotard@foss.st.com


Signed-off-by: Rob Herring <robh@kernel.org>