Fix typo in the script

Signed-off-by: Anton Kolesov <Anton.Kolesov@synopsys.com>
Proper solution for broken networking

Previous patch acb6f86 didn't worked as expected because SERIAL_OF_PLATFORM
has dependencies which were not satisfied. This patch provides a proper
defconfig that will really enable SERIAL_OF_PLATFORM.

Signed-off-by: Anton Kolesov <Anton.Kolesov@synopsys.com>