rsi: rsi_91x_ps: remove redundant code in str_psstate

"INVALID_STATE" is already being returned in the default case and this
code cannot be reached.

Addresses-Coverity-ID: 1398384
Signed-off-by: Gustavo A. R. Silva <garsilva@embeddedor.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>

drivers/net/wireless/rsi/rsi_91x_ps.c

@@ -36,7 +36,6 @@ char *str_psstate(enum ps_state state)
 	default:
 		return "INVALID_STATE";
 	}
-	return "INVALID_STATE";
 }
 
 static inline void rsi_modify_ps_state(struct rsi_hw *adapter,