tpm2: Require TPM_NV_DISK to avoid case of tpm_stata_path being NULL

Address an issue reported by cppcheck that raises the issue that
tpm_state_path could be NULL when the #define TPM_NV_DISK is not set.
Require that the #define TPM_NV_DISK always be set.

Resolves: https://github.com/stefanberger/libtpms/issues/313
Signed-off-by: Stefan Berger <stefanb@linux.ibm.com>

src/tpm_nvfile.c

@@ -123,6 +123,8 @@ TPM_RESULT TPM_NVRAM_Init(void)
             rc = TPM_FAIL;
         }
     }
+#else
+# error TPM_NV_DISK must be defined
 #endif
     /* check that the directory name plus a file name will not overflow FILENAME_MAX */
     if (rc == 0) {