Fixes and improvements log options save/restore methods
- device prefix size needed update, but now using log function name instead
- don't use overlapping strcpy() (increment pointer and one single strcpy())
- now using get_logfn_id() to simplify code
TODO: fix floppy access failure after restore


git-svn-id: svn://svn.code.sf.net/p/bochs/code/trunk@12324 6c8e4198-a580-4521-a02f-c9ae86df1db9