srd_inst_option_set(): Fix multiple memory leaks.

srd_inst_option_set(): Fix multiple memory leaks.

These were reported when compiling with "-fsanitize=address" and running
"PYTHONMALLOC=malloc make check":

  =================================================================
  ==42879==ERROR: LeakSanitizer: detected memory leaks

  Direct leak of 317 byte(s) in 6 object(s) allocated from:
      #0 0x7f08e4809538 in __interceptor_malloc ../../../../src/libsanitizer/asan/asan_malloc_linux.cc:144
      #1 0x7f08e3f37622 in PyUnicode_New ../Objects/unicodeobject.c:1365

  Direct leak of 28 byte(s) in 1 object(s) allocated from:
      #0 0x7f08e4809538 in __interceptor_malloc ../../../../src/libsanitizer/asan/asan_malloc_linux.cc:144
      #1 0x7f08e3f7e1a5 in _PyLong_New ../Objects/longobject.c:275

  Direct leak of 24 byte(s) in 1 object(s) allocated from:
      #0 0x7f08e4809538 in __interceptor_malloc ../../../../src/libsanitizer/asan/asan_malloc_linux.cc:144
      #1 0x7f08e3f91521 in PyFloat_FromDouble ../Objects/floatobject.c:122

  SUMMARY: AddressSanitizer: 369 byte(s) leaked in 8 allocation(s).
   session