drivers: char: mem: fix IS_ERROR_VALUE usage

IS_ERR_VALUE macro should be used only with unsigned long type.
Specifically it works incorrectly with longer types.

The patch follows conclusion from discussion on LKML [1][2].

[1]: http://permalink.gmane.org/gmane.linux.kernel/2120927
[2]: http://permalink.gmane.org/gmane.linux.kernel/2150581

Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
Acked-by: Al Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/char/mem.c

@@ -695,7 +695,7 @@ static loff_t memory_lseek(struct file *file, loff_t offset, int orig)
 		offset += file->f_pos;
 	case SEEK_SET:
 		/* to avoid userland mistaking f_pos=-9 as -EBADF=-9 */
-		if (IS_ERR_VALUE((unsigned long long)offset)) {
+		if ((unsigned long long)offset >= -MAX_ERRNO) {
 			ret = -EOVERFLOW;
 			break;
 		}