EDAC/igen6: Return the correct error type when not the MC owner

Return -EBUSY instead of -ENODEV just like the other EDAC drivers do.

  [ bp: Rewrite text. ]

Signed-off-by: Jia He <justin.he@arm.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lore.kernel.org/r/20221018082214.569504-8-justin.he@arm.com