ras/debugfs: Fix error checking for debugfs_create_dir()

Check the return value of debugfs_create_dir() properly.

  [ bp: Rewrite commit message. ]

Signed-off-by: Osama Muhammad <osmtendev@gmail.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20230516182927.9171-1-osmtendev@gmail.com