powerpc/xmon: fix dump_segments()

powerpc/xmon: fix dump_segments()

BugLink: https://bugs.launchpad.net/bugs/1855787
[ Upstream commit 32c8c4c621897199e690760c2d57054f8b84b6e6 ]

mfsrin() takes segment num from bits 31-28 (IBM bits 0-3).

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
[mpe: Clarify bit numbering]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>