Add check for valid Chip ID and fail early

Confused myself by plugging this into a BG base. It gave all the appearance of working, but the time was not counting up.
Turns out the library will happily talk to no device whatsoever and when you "set_time" it's stored in an C array and returned as if it came from the RTC.

drivers/rv3028/rv3028.cpp

@@ -74,6 +74,12 @@ namespace pimoroni {
       gpio_pull_up(interrupt);
     }
 
+    uint8_t chip_id = 0;
+    read_bytes(RV3028_ID, &chip_id, 1);
+    if(chip_id != (RV3028_CHIP_ID | RV3028_VERSION)) {
+      return false;
+    }
+
     return true;
   }
 

drivers/rv3028/rv3028.hpp

@@ -84,6 +84,8 @@ Distributed as-is; no warranty is given.
 
 //ID register
 #define RV3028_ID                0x28
+#define RV3028_CHIP_ID           0x30
+#define RV3028_VERSION           0x03
 
 //EEPROM Registers
 #define EEPROM_Clkout_Register        0x35

examples/breakout_rtc/demo.cpp

@@ -12,7 +12,9 @@ int main() {
   gpio_init(PICO_DEFAULT_LED_PIN);
   gpio_set_dir(PICO_DEFAULT_LED_PIN, GPIO_OUT);
 
-  rtc.init();
+  if(!rtc.init()) {
+    printf("Init failed! Check your connections and i2c pin choices.\n");
+  }
   // rtc.setup(false);
 
   // Uncomment the below line on first run to set the RTC date and time to the program's compiler time