Fix srec issue

[schneidersoft]

Fixes #162 as well as some other older issues

[spth]

I get the same error as @konstz43:

srec.c: In function ‘load_srec’:
srec.c:92:38: error: ‘addrmin’ undeclared (first use in this function); did you mean ‘addrmax’?
   92 |         const unsigned int addrmax = addrmin + data_len;
      |                                      ^~~~~~~
      |                                      addrmax