perf probe: Fix getting the kernel map

perf probe: Fix getting the kernel map

Since commit 4d99e4136580 ("perf machine: Workaround missing maps for
x86 PTI entry trampolines"), perf tools has been creating more than one
kernel map, however 'perf probe' assumed there could be only one.

Fix by using machine__kernel_map() to get the main kernel map.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Tested-by: Joseph Qi <joseph.qi@linux.alibaba.com>
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jiufei Xue <jiufei.xue@linux.alibaba.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: stable@vger.kernel.org
Cc: Xu Yu <xuyu@linux.alibaba.com>
Fixes: 4d99e4136580 ("perf machine: Workaround missing maps for x86 PTI entry trampolines")
Fixes: d83212d5dd67 ("kallsyms, x86: Export addresses of PTI entry trampolines")
Link: http://lkml.kernel.org/r/2ed432de-e904-85d2-5c36-5897ddc5b23b@intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>