EDAC/mem_repair: Reduce stack usage in edac_mem_repair_get_desc()

Constructing an array on the stack adds complexity and can exceed the
warning limit for per-function stack usage:

  drivers/edac/mem_repair.c:361:5: error: stack frame size (1296) exceeds
  limit (1280) in 'edac_mem_repair_get_desc' [-Werror,-Wframe-larger-than]

Change this to have the actual attribute array allocated statically and then
just add the instance number on the per-instance copy.

Fixes: 699ea521 ("EDAC: Add a memory repair control feature")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/20250620114135.4017183-1-arnd@kernel.org