firmware_loader: Update contact emails for ABI docs

Update the firmware_loader documentation and corresponding section
in the MAINTAINERs file with a new email address.

Signed-off-by: Russ Weight <russell.h.weight@intel.com>
Link: https://lore.kernel.org/r/20230929151326.311959-1-russell.h.weight@intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>