rp: fix blocking I2C example regarding pull-up resistors

This amends the blocking I2C example for embassy-rp.

Commit bbc3e49 added a pull-up configuration and a comment that pull-ups
were not enabled by default. This was made out-of-date by badcdcc, which
ensured pull-ups were enabled by default to make the larger I2C
configuration change non-breaking.

This commit removes the (now-unnecessary) pull-up configuration, and
adds a comment to clarify that the default I2C configuration enables
pull-ups.

Author: robjwells

examples/rp/src/bin/i2c_blocking.rs

@@ -49,10 +49,8 @@ async fn main(_spawner: Spawner) {
     let scl = p.PIN_15;
 
     info!("set up i2c ");
-    let mut config = Config::default();
-    // by default internal pullup resitors are disabled
-    config.sda_pullup = true;
-    config.scl_pullup = true;
+    // Default I2C config enables internal pull-up resistors.
+    let config = Config::default();
     let mut i2c = i2c::I2c::new_blocking(p.I2C1, scl, sda, config);
 
     use mcp23017::*;