powerpc: fix dead default for GUEST_STATE_BUFFER_TEST

powerpc: fix dead default for GUEST_STATE_BUFFER_TEST

The GUEST_STATE_BUFFER_TEST config option should default
to KUNIT_ALL_TESTS so that if all tests are enabled then
it is included, but currently the 'default KUNIT_ALL_TESTS'
statement is shadowed by 'def_tristate n',
meaning that this second default statement is currently dead code.

It looks to me like the commit
6ccbbc33f06a ("KVM: PPC: Add helper library for Guest State Buffers")
intended to set the default to KUNIT_ALL_TESTS, but mistakenly
missed the def_tristate.

This dead code was found by kconfirm, a static analysis tool for Kconfig.

Fixes: 6ccbbc33f06a ("KVM: PPC: Add helper library for Guest State Buffers")
Signed-off-by: Julian Braha <julianbraha@gmail.com>
Tested-by: Gautam Menghani <gautam@linux.ibm.com>
Reviewed-by: Amit Machhiwal <amachhiw@linux.ibm.com>
Reviewed-by: Harsh Prateek Bora <harshpb@linux.ibm.com>
Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Link: https://patch.msgid.link/20260405161545.161006-1-julianbraha@gmail.com