nios2: fixed variable imm16 to s16

Fxid variable imm16 to s16 instead of u16, offset might be negative.
Signed-off-by: Bernd Weiberg <bernd.weiberg@siemens.com>
Signed-off-by: Ley Foon Tan <lftan@altera.com>

arch/nios2/kernel/misaligned.c

@@ -71,7 +71,7 @@ asmlinkage void handle_unaligned_c(struct pt_regs *fp, int cause)
 	u32 isn, addr, val;
 	int in_kernel;
 	u8 a, b, d0, d1, d2, d3;
-	u16 imm16;
+	s16 imm16;
 	unsigned int fault;
 
 	/* back up one instruction */