dt-bindings: rp2350: correct PWM names for GPIOs 40..47

The macros for PWM output on these GPIOs had names that referred to PWM
channels that do no exist on this chip- it only has 12 channels, where
channels 8..11 are exposed on both GPIOs 32..39 and 40..47.

Signed-off-by: Peter Marheine <peter@taricorp.net>