Include the file name to open and the fail error number

Also fix issues reported by nxstyle

examples/sx127x_demo/sx127x_demo.c

@@ -362,6 +362,7 @@ static void print_hex(uint8_t *data, int len)
             }
         }
     }
+
   printf("\n");
 }
 
@@ -483,7 +484,8 @@ int main(int argc, FAR char *argv[])
   fd = open(DEV_NAME, O_RDWR);
   if (fd < 0)
     {
-      printf("ERROR: Failed to open device!\n");
+      int errcode = errno;
+      printf("ERROR: Failed to open device %s: %d\n", DEV_NAME, errcode);
       goto errout;
     }