x86/dumpstack: Avoid uninitlized variable

In some configurations, 'partial' does not get initialized, as shown by
this gcc-8 warning:

arch/x86/kernel/dumpstack.c: In function 'show_trace_log_lvl':
arch/x86/kernel/dumpstack.c:156:4: error: 'partial' may be used uninitialized in this function [-Werror=maybe-uninitialized]
    show_regs_if_on_stack(&stack_info, regs, partial);
    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

This initializes it to false, to get the previous behavior in this case.

Fixes: a9cdbe72 ("x86/dumpstack: Fix partial register dumps")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Nicolas Pitre <nico@linaro.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Borislav Petkov <bpetkov@suse.de>
Cc: Vlastimil Babka <vbabka@suse.cz>
Link: https://lkml.kernel.org/r/20180202145634.200291-1-arnd@arndb.de

arch/x86/kernel/dumpstack.c

@@ -109,7 +109,7 @@ void show_trace_log_lvl(struct task_struct *task, struct pt_regs *regs,
 	struct stack_info stack_info = {0};
 	unsigned long visit_mask = 0;
 	int graph_idx = 0;
-	bool partial;
+	bool partial = false;
 
 	printk("%sCall Trace:\n", log_lvl);