arch/i386/mm/fault.c: fix sparse warnings

Index: linux-2.6.11-bk1-sparse/arch/i386/mm/fault.c
===================================================================
@@ -146,7 +146,7 @@ static int __is_prefetch(struct pt_regs 
 
 		if (instr > limit)
 			break;
-		if (__get_user(opcode, (unsigned char *) instr))
+		if (__get_user(opcode, (unsigned char __user *) instr))
 			break; 
 
 		instr_hi = opcode & 0xf0; 

@@ -173,7 +173,7 @@ static int __is_prefetch(struct pt_regs 
 			scan_more = 0;
 			if (instr > limit)
 				break;
-			if (__get_user(opcode, (unsigned char *) instr)) 
+			if (__get_user(opcode, (unsigned char __user *) instr)) 
 				break;
 			prefetch = (instr_lo == 0xF) &&
 				(opcode == 0x0D || opcode == 0x18);