new helpers: no_seek_end_llseek{,_size}()

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

drivers/usb/misc/sisusbvga/sisusb.c

@@ -2825,21 +2825,7 @@ sisusb_lseek(struct file *file, loff_t offset, int orig)
 		return -ENODEV;
 	}
 
-	switch (orig) {
-		case 0:
-			file->f_pos = offset;
-			ret = file->f_pos;
-			/* never negative, no force_successful_syscall needed */
-			break;
-		case 1:
-			file->f_pos += offset;
-			ret = file->f_pos;
-			/* never negative, no force_successful_syscall needed */
-			break;
-		default:
-			/* seeking relative to "end of file" is not supported */
-			ret = -EINVAL;
-	}
+	ret = no_seek_end_llseek(file, offset, orig);
 
 	mutex_unlock(&sisusb->lock);
 	return ret;