Documentation/EDAC: Fix warning document isn't included in any toctree

Fix the build (htmldocs) warning:

  Documentation/edac/index.rst: WARNING: document isn't included in any toctree.

Fixes: db99ea5 ("EDAC: Add support for EDAC device features control")
Closes: https://lore.kernel.org/all/20250228185102.15842f8b@canb.auug.org.au/
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Shiju Jose <shiju.jose@huawei.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20250401115823.573-1-shiju.jose@huawei.com

Author: shijujose4

Documentation/subsystem-apis.rst

@@ -71,6 +71,7 @@ Other subsystems
 
    accounting/index
    cpu-freq/index
+   edac/index
    fpga/index
    i2c/index
    iio/index