sscanf: don't ignore field widths for numeric conversions

sscanf: don't ignore field widths for numeric conversions

This is another step towards better standard conformance.  Rather than
adding a local buffer to store the specified portion of the string (with
the need to enforce an arbitrary maximum supported width to limit the
buffer size), do a maximum width conversion and then drop as much of it as
is necessary to meet the caller's request.

Also fail on negative field widths.

Uses the deprecated simple_strto*() functions because kstrtoXX() fail on
non-zero terminated strings.

Signed-off-by: Jan Beulich <[email protected]>
Cc: Alexey Dobriyan <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>