checkpatch: add an index variable for fixed lines

Make the fix code a bit easier to read.

This should also start to allow an easier mechanism to insert/delete
lines eventually too.

Signed-off-by: Joe Perches <[email protected]>
Cc: Andy Whitcroft <[email protected]>
Cc: Dan Carpenter <[email protected]>
Cc: Josh Triplett <[email protected]>
Cc: Greg Kroah-Hartman <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>