ieee802154: fix new function declaration

The commit 8fad346f ("eee802154: add basic support for RF212 to
at86rf230 driver") introduced the new function is_rf212() with some
minor issues in declaration:

1) Fix the function type by changing it to bool as the function
   definition returns a boolean value. Additionally both callers of
   is_rf212() are expected to return a boolean value.

2) Fix the function specifier by deleting the inline keyword as the
   compiler takes care of that.
Signed-off-by: NJean Sacren <sakiwit@gmail.com>
Cc: Phoebe Buckheister <phoebe.buckheister@itwm.fraunhofer.de>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ieee802154/at86rf230.c

@@ -57,7 +57,7 @@ struct at86rf230_local {
 	int rssi_base_val;
 };
 
-static inline int is_rf212(struct at86rf230_local *local)
+static bool is_rf212(struct at86rf230_local *local)
 {
 	return local->part == 7;
 }