perf: fix for rebuilding

Fix for rebuilding error:
make[3]: *** No rule to make target `/path/to/sysroots/qemuarm64/usr/src/kernel/tools/lib/traceevent//trace-seq.c',
needed by `.trace-seq.d'.  Stop.
make[2]: *** [sub-make] Error 2

(From OE-Core rev: 9dafa571ed0a40d21a886dec7704c31150b21942)

Signed-off-by: Robert Yang <liezhi.yang@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/recipes-kernel/perf/perf.bb

@@ -115,6 +115,10 @@ do_install() {
 }
 
 do_configure_prepend () {
+    # Fix for rebuilding
+    rm -rf ${B}/
+    mkdir ${B}/
+
     #kernels before 3.1 do not support WERROR env variable
     sed -i 's,-Werror ,,' ${S}/tools/perf/Makefile
     if [ -e "${S}/tools/perf/config/Makefile" ]; then