config: don't define the same symbol twice

config: don't define the same symbol twice

In commit fce35bce0f6e ("config: support new symbol intro'd in kernel
4.12")
I forgot to remove the initial debug test line.

This clearly is wrong as the same symbol is defined conditionally in the
line below as it should be.

I looked over it as I just checked if the symbol was present now upon
testing it.

Fixes: fce35bce0f6e ("config: support new symbol intro'd in kernel
4.12")

Signed-off-by: Koen Vandeputte <koen.vandeputte@ncentric.com>