package.bbclass: Do not hide cpio's error

package.bbclass: Do not hide cpio's error

We use subprocess.check_output() to run the command, which means that we need care
about the error, so the 2>/dev/null should not be used, otherwise it is hard to
debug when the error happens.

I guess it was copied from previous lines, but that command's error can be
ignored (excpet: pass):
   try:
       subprocess.check_output(cmd, shell=True, stderr=subprocess.STDOUT)
   except subprocess.CalledProcessError:
       # Can "fail" if internal headers/transient sources are attempted
       pass

But we don't do this in the current location, so remove "2>/dev/null"

(From OE-Core rev: 017a53d2743be2b5d4965a39b4e126fb74f700ad)

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