i2c: Set ack bit on multibyte reads

Enable the ack bit on multibyte (>2) reads otherwise bytes from the
remote device are not acknowledged.

Signed-off-by: Sjoerd Simons <sjoerd@luon.net>

src/i2c.rs

@@ -533,6 +533,7 @@ where
                 self.nb.i2c.cr1.modify(|_, w| w.ack().set_bit());
             }
             buffer_len => {
+                self.nb.i2c.cr1.modify(|_, w| w.ack().set_bit());
                 self.nb.i2c.sr1.read();
                 self.nb.i2c.sr2.read();