mips/boston: Fix boston_mach_init() error handling

mips/boston: Fix boston_mach_init() error handling

The Error ** argument must be NULL, &error_abort, &error_fatal, or a
pointer to a variable containing NULL.  Passing an argument of the
latter kind twice without clearing it in between is wrong: if the
first call sets an error, it no longer points to NULL for the second
call.

boston_mach_init() is wrong that way.  The last calls treats an error
as fatal.  Do that for the prior ones, too.

Fixes: df1d8a1f29f567567b9d20be685a4241282e7005
Cc: Paul Burton <pburton@wavecomp.com>
Cc: Aleksandar Rikalo <aleksandar.rikalo@rt-rk.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20200505101908.6207-8-armbru@redhat.com>
Reviewed-by: Aleksandar Markovic <aleksandar.qemu.devel@gmail.com>