perf symbols: Load map before using map->map_ip()

In map_groups__find_symbol() map->map_ip is used without ensuring the
map is loaded. Then the address passed to map->map_ip isn't mapped at
the first time.

E.g. below code always fails to get a symbol at the first call;

	addr = /* Somewhere in the kernel text */
	symbol_conf.try_vmlinux_path = true;
	symbol__init();
	host_machine = machine__new_host();
	sym = machine__find_kernel_function(host_machine,
					 addr, NULL, NULL);
	/* Note that machine__find_kernel_function calls
	   map_groups__find_symbol */

This ensures it by calling map__load before using it in
map_groups__find_symbol().

Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: "David A. Long" <dave.long@linaro.org>
Cc: David Ahern <dsahern@gmail.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: "Steven Rostedt (Red Hat)" <rostedt@goodmis.org>
Cc: yrl.pp-manager.tt@hitachi.com
Link: http://lkml.kernel.org/r/20140123022950.7206.17357.stgit@kbuild-fedora.yrl.intra.hitachi.co.jp


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>