EDAC/igen6: Reduce log level to debug for absent memory controllers

The current KERN_WARNING level message for detecting absent memory
controllers is overly dramatic. The BIOS likely had valid reasons to
disable the memory controller (e.g. it isn't connected to any DIMM
slots on the motherboard for this system). So there's nothing actually
wrong that needs to be fixed.

Reduce the log level to KERN_DEBUG to eliminate the false warning.

Suggested-by: Tony Luck <tony.luck@intel.com>
Signed-off-by: Qiuxu Zhuo <qiuxu.zhuo@intel.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20250618162307.1523736-2-qiuxu.zhuo@intel.com