Panic rather than BUG if an error is encountered decompressing a bzImage

This gives a more useful error message without an unnecessary stack dump.

Noticed by Jeremy Fitzhardinge.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>

xen/arch/x86/bzimage.c

@@ -58,8 +58,7 @@ static void flush_window(void);
 
 static __init void error(char *x)
 {
-    printk("%s\n", x);
-    BUG();
+    panic("%s\n", x);
 }
 
 static __init int fill_inbuf(void)