kernel: use show_stack_loglvl()

Align the last users of show_stack() by KERN_DEFAULT as the surrounding
headers/messages.

Signed-off-by: Dmitry Safonov <dima@arista.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Will Deacon <will@kernel.org>
Link: http://lkml.kernel.org/r/20200418201944.482088-50-dima@arista.com


Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>