kconfig: recalc symbol value before showing search results

A symbol's value won't be recalc-ed until we save config file or
enter the menu where the symbol sits.

So If I enable OPTIMIZE_FOR_SIZE, and search FUNCTION_GRAPH_TRACER:

  Symbol: FUNCTION_GRAPH_TRACER [=y]
  Prompt: Kernel Function Graph Tracer
    Defined at kernel/trace/Kconfig:140
    Depends on: ... [=y] && (!X86_32 [=y] || !CC_OPTIMIZE_FOR_SIZE [=y])
    ...

From the dependency it should result in FUNCTION_GRAPH_TRACER=n,
but it still shows FUNCTION_GRAPH_TRACER=y.

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Signed-off-by: Michal Marek <mmarek@suse.cz>