[PARISC] dump_stack in show_regs

Originally, show_stack was used in BUG() output. However, a recent commit
changed it to print register state (no idea what that's supposed to help,
really...) and parisc was missing a backtrace because of it.
Signed-off-by: Kyle McMartin <kyle@parisc-linux.org>

arch/parisc/kernel/traps.c

@@ -148,6 +148,8 @@ void show_regs(struct pt_regs *regs)
 	print_symbol(" IAOQ[1]: %s\n", regs->iaoq[1]);
 	printk(level);
 	print_symbol(" RP(r2): %s\n", regs->gr[2]);
+
+	dump_stack();
 }