staging: add missing import errno to staging_populate_sysroot_dir

Fixes error "Exception: NameError: name 'errno' is not defined"
during build-sysroots.bb:do_build_target_sysroot

(From OE-Core rev: b1e482ae20b9c714f4089d4da6470d041242e441)

Signed-off-by: Marko, Peter <peter.marko@siemens.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/classes/staging.bbclass

@@ -177,6 +177,7 @@ def staging_processfixme(fixme, target, recipesysroot, recipesysrootnative, d):
 def staging_populate_sysroot_dir(targetsysroot, nativesysroot, native, d):
     import glob
     import subprocess
+    import errno
 
     fixme = []
     postinsts = []