Staging: rtl8188eu: Fix warning of kfree check is not required.

This patch fixes the warning produced by checkpatch in the file
rtw_cmd.c "kfree(NULL) is safe this check is probably not required". The
patch fixes it in two places for this file.

Signed-off-by: Elena Oat <oat.elena@gmail.com>
Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>