powerpc/xive: fix return value of __setup handler

__setup() handlers should return 1 to obsolete_checksetup() in
init/main.c to indicate that the boot option has been handled.

A return of 0 causes the boot option/value to be listed as an Unknown
kernel parameter and added to init's (limited) argument or environment
strings.

Also, error return codes don't mean anything to obsolete_checksetup() --
only non-zero (usually 1) or zero. So return 1 from xive_off() and
xive_store_eoi_cmdline().

Fixes: 243e2511 ("powerpc/xive: Native exploitation of the XIVE interrupt controller")
Fixes: c21ee04f ("powerpc/xive: Add a kernel parameter for StoreEOI")
[lore.kernel.org/r/64644a2f-4a20-bab3-1e15-3b2cdd0defe3@omprussia.ru]
Reported-by: Igor Zhbanov <i.zhbanov@omprussia.ru&gt;:>
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Reviewed-by: Cédric Le Goater <clg@kaod.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220313065936.4363-1-rdunlap@infradead.org