x86/amd_gart: print stacktrace for a leak with KERN_ERR

It's under CONFIG_IOMMU_LEAK option which is enabled by debug config.
Likely the backtrace is worth to be seen - so aligning with log level of
error message in iommu_full().

Signed-off-by: Dmitry Safonov <dima@arista.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20200418201944.482088-46-dima@arista.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/x86/kernel/amd_gart_64.c

@@ -159,7 +159,7 @@ static void dump_leak(void)
 		return;
 	dump = 1;
 
-	show_stack(NULL, NULL);
+	show_stack_loglvl(NULL, NULL, KERN_ERR);
 	debug_dma_dump_mappings(NULL);
 }
 #endif