EDAC/mc: Get rid of silly one-shot struct allocation in edac_mc_alloc()

This has probably meant something at some point but there's no need for
it anymore - the struct mem_ctl_info allocation can happen with normal,
boring k*alloc() calls like everyone else does it.

No functional changes.

Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lore.kernel.org/r/20220310095254.1510-2-bp@alien8.de