Update README.md

Another small typo in documentation

Author: hpcraink

src/rp2350/README.md

@@ -1,5 +1,5 @@
 This directory contains files specific to the RP2350 hardware. It is only used when building for RP2350 platforms, i.e. 
-`PICO_PLATFORM=rp2350-arm-s` or `PICO_PLATFORM=rp235-riscv`
+`PICO_PLATFORM=rp2350-arm-s` or `PICO_PLATFORM=rp2350-riscv`
 
 `hardware_regs` contains low level hardware register #defines autogenerated from the RP2350 chip definition itself.