perf: fail if src path does not exist

A missing src directory from a broken kernel recipe resulted
only in a warning:

WARNING: copyfile: stat of /home/builder/src/tmp-glibc/work-shared/target/kernel-source/tools/arch failed ([Errno 2] No such file or directory: '/home/builder/src/tmp-glibc/work-shared/target/kernel-source/tools/arch')

and the build failed horribly.

With this change it's an error which can not be missed:

ERROR: perf-1.0-r9 do_configure: Path does not exist: /home/builder/src/tmp-glibc/work-shared/target/kernel-source/tools/arch. Maybe PERF_SRC does not match the kernel version.
ERROR: perf-1.0-r9 do_configure: Function failed: copy_perf_source_from_kernel
ERROR: Logfile of failure stored in: /home/builder/src/tmp-glibc/work/target-linux/perf/1.0-r9/temp/log.do_configure.21083
NOTE: recipe perf-1.0-r9: task do_configure: Failed
ERROR: Task (/home/builder/src/poky/meta/recipes-kernel/perf/perf.bb:do_configure) failed with exit code '1'

To get get perf compiling from a custom kernel, a perf.bbappend can be
created which defines PERF_SRC as list of files and directories needed
from kernel source tree to compile perf. This varies between kernel
versions.

(From OE-Core rev: c392dabefc431dbfb31d6a1465c75ba9cc765804)

Signed-off-by: Mikko Rapeli <mikko.rapeli@bmw.de>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/recipes-kernel/perf/perf.bb

@@ -147,6 +147,8 @@ python copy_perf_source_from_kernel() {
     for s in sources:
         src = oe.path.join(src_dir, s)
         dest = oe.path.join(dest_dir, s)
+        if not os.path.exists(src):
+            bb.fatal("Path does not exist: %s. Maybe PERF_SRC does not match the kernel version." % src)
         if os.path.isdir(src):
             oe.path.copyhardlinktree(src, dest)
         else: