myri10ge: use ioremap_wc

Switch to ioremap_wc(). We keep the MTRR code since ioremap_wc()
will use UC_MINUS when falling back to uncachable, and thus let
the MTRR WC take precedence.

Also rename the error path better.

Signed-off-by: Brice Goglin <brice@myri.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>