sh: dump_stack: Fix broken lines and ptrval in calltrace dumps

Rejoin the broken lines by dropping the log level parameters and using
pr_cont().
Use "%px" to print sensible addresses in call traces.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Tested-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Rich Felker <dalias@libc.org>