bitbake: utils: Fix mkdir with PosixPath

Avoid:
    Exception: AttributeError: 'PosixPath' object has no attribute 'find'

(Bitbake rev: 0b37fe89ba12549109905b6d0e6d07d342162436)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/lib/bb/utils.py

@@ -759,7 +759,7 @@ def mkdirhier(directory):
     """Create a directory like 'mkdir -p', but does not complain if
     directory already exists like os.makedirs
     """
-    if directory.find('${') != -1:
+    if '${' in str(directory):
         bb.fatal("Directory name {} contains unexpanded bitbake variable. This may cause build failures and WORKDIR polution.".format(directory))
     try:
         os.makedirs(directory)