The function adf_dbgfs_exit() was improperly named causing the build to
fail when CONFIG_DEBUG_FS=n.

Rename adf_dbgfs_cleanup() as adf_dbgfs_exit().

This fixes the following build error:
      CC [M]  drivers/crypto/intel/qat/qat_c62x/adf_drv.o
    drivers/crypto/intel/qat/qat_c62x/adf_drv.c: In function ‘adf_cleanup_accel’:
    drivers/crypto/intel/qat/qat_c62x/adf_drv.c:69:9: error: implicit declaration of function ‘adf_dbgfs_exit’; did you mean ‘adf_dbgfs_init’? [-Werror=implicit-function-declaration]
       69 |         adf_dbgfs_exit(accel_dev);
          |         ^~~~~~~~~~~~~~
          |         adf_dbgfs_init
    cc1: all warnings being treated as errors
    make[2]: *** [scripts/Makefile.build:252: drivers/crypto/intel/qat/qat_c62x/adf_drv.o] Error 1
    make[1]: *** [scripts/Makefile.build:494: drivers/crypto/intel/qat/qat_c62x] Error 2
    make: *** [Makefile:2026: drivers/crypto/intel/qat] Error 2

Fixes: 9260db66 ("crypto: qat - move dbgfs init to separate file")
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202306030654.5t4qkyN1-lkp@intel.com/Signed-off-by: Giovanni Cabiddu <giovanni.cabiddu@intel.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>