Correct two typos (#2648)

* Update sha256_alt.h

Fix trivial copy-paste error in comment

* 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.
 

src/rp2_common/pico_mbedtls/include/sha256_alt.h

@@ -11,6 +11,6 @@
 #include "pico/sha256.h"
 
 typedef struct pico_sha256_state mbedtls_sha256_context;
-#endif // PICO_RP2350
+#endif // LIB_PICO_SHA256
 
 #endif