scripts/log_parser: Handle signed and unsigned char length modifier

The C standard specifies 'hh' as a length modifier indicating an integer
conversion specifier applies to a signed char or unsigned char
argument. Python doesn't do that, so replace relevant %hh with %h.

Also fix the handling of %ll so that it applies to all integer specifiers
as well.

Signed-off-by: Keith Packard <keithp@keithp.com>