x86/dumpstack: Combine some printk()s

Long ago, Jiri Slaby noted that the subsequent printk()s should be
pr_cont(). Let's instead get rid of the multiple printk calls.

Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Jiri Slaby <jslaby@suse.cz>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1459024817-27122-1-git-send-email-linux@rasmusvillemoes.dk
Signed-off-by: Ingo Molnar <mingo@kernel.org>