Replace strtok with strtok_r

strtok is deprecated.

frameworks/av/media/libmediahelper/include/media/TypeConverter.h:172:29: warning: 'strtok' is deprecated: strtok() is not thread-safe; use strtok_r() instead [-Wdeprecated-declarations]
  172 |     for (const char *cstr = strtok(literal, del); cstr != NULL; cstr = strtok(NULL, del)) {
      |

Test: presubmit
Flag: EXEMPT, code cleanup
Change-Id: I56a29fbdd9325160f7a13375013e663d01dc9c49