oct612x: Build failure due to EXTRA_CFLAGS being removed in the kernel

[InterLinked1]

Support for EXTRA_CFLAGS has been removed in the kernel, rendering the Kbuild and Makefile for the oct612x library invalid. This now manifests as a build failure due to the missing options:

  CC [M]  oct612x/octdeviceapi/oct6100api/oct6100_api/oct6100_adpcm_chan.o
oct612x/octdeviceapi/oct6100api/oct6100_api/oct6100_adpcm_chan.c:34:10: fatal error: octdef.h: No such file or directory
   34 | #include "octdef.h"
      |          ^~~~~~~~~~
compilation terminated.
make[5]: *** [/usr/src/linux-next/scripts/Makefile.build:203: oct612x/octdeviceapi/oct6100api/oct6100_api/oct6100_adpcm_chan.o] Error 1
make[4]: *** [/usr/src/linux-next/scripts/Makefile.build:461: oct612x] Error 2