Fix "map" OpenFirmware call. It does not return a value according to the

Fix "map" OpenFirmware call.  It does not return a value according to the
IEEE 1275 specification.  This should fix booting on machines that would
fail with something like:

OF_map_phys(3fe44000,8192,fed58000,-1) failed
no space for symbol table
Program terminated

Based on a diff provided by Harald Gutch (hgutch@netbsd).  Also see
NetBSD PR#56829.

There were (and still are) some questions about whether this diff breaks
the blade1.5k. However the failure in question might have been hardware
related and subsequent testing of the equivalent kernel diff (which
was just committed) was successful.  So committing this in the hope it
sticks to ease testing.

ok miod@