Update sfe_bus.cpp for Particle Platform

I haven't done much platform porting so I'm not exactly sure the most correct way to fix this, but casting data uint8_t* to char* resolves the compiler error:
 invalid conversion from 'uint8_t*' {aka 'unsigned char*'} to 'char*' 

I would guess the right next step is to dig into DeviceOS serial handling but maybe someone can comment.

If this is an acceptable solution, or if it's safe to cast to char * for all platforms I'd like to see it merge into main so I don't have to remember it in the future.

Author: niabassey

src/sfe_bus.cpp

@@ -464,7 +464,10 @@ namespace SparkFun_UBLOX_GNSS
 
     if (length == 0)
       return 0;
-
+#ifdef PARTICLE
+    return _serialPort->readBytes((char *)data, length);
+#else
     return _serialPort->readBytes(data, length);
+#endif
   }
 }