Move local variables to inner block

Move local variables to inner block

dummy_frame_sniffer has two local variables dummyframe and this_id,
but they are only used in the if block below.  This patch is to move
them into the inner block.

gdb:

2014-06-26  Yao Qi  <yao@codesourcery.com>

	* dummy-frame.c (dummy_frame_sniffer): Move local variables
	dummyframe and this_id into inner block below.