i5000: Fix the fatal error handling

The fatal error channel bits point to a single channel, and not
to a range of channels. Fix the code to properly report it,
instead of printing messages like:
	kernel: EDAC MC0: INTERNAL ERROR: channel-b out of range (4 >= 4)

Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>