fix: Update WBADFILE definition to use NULL

Co-Authored-By: [email protected] <[email protected]>

Author: devin-ai-integration[bot]

.github/workflows/fatfs-check.yml

@@ -85,7 +85,7 @@ jobs:
           echo "#undef WOLFSSH_USER_FILESYSTEM" >> ${{ github.workspace }}/build-dir/include/wolfssh/myFilesystem.h
           echo "#include <ffconf.h>" >> ${{ github.workspace }}/build-dir/include/wolfssh/myFilesystem.h
           echo "#include <ff.h>" >> ${{ github.workspace }}/build-dir/include/wolfssh/myFilesystem.h
-          echo "#define WBADFILE ((FIL*)0)" >> ${{ github.workspace }}/build-dir/include/wolfssh/myFilesystem.h
+          echo "#define WBADFILE NULL" >> ${{ github.workspace }}/build-dir/include/wolfssh/myFilesystem.h
 
       - name: Checkout, build, and test wolfssh
         uses: wolfSSL/actions-build-autotools-project@v1