SVF: fix parsing hex strings containing leading '0' characters

Ignore leading '0' characters on hex strings.  For example a bit
pattern consisting of 6 bits could be written as 3f, 03f or 003f and
so on.

Signed-off-by: Michael Roth <mroth@nessie.de>
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>