MLBEDSW-7542: Fix output diff caused by wrong scaling in Conv2d

- The reference calculates the scale slightly different between
Conv2d and FullyConnect. Recently a fix was submitted to address
this issue. However, internally a Conv2d can be changed to a
FullyConnect but then the scale must still be calculated
following the Conv2d reference.

- The fix is to check the original type if FullyConnect scale
should be used or not.

Change-Id: I5a9fb49126f0df63712b73fb5520fdc604cee378
Signed-off-by: Johan Alfven <johan.alfven@arm.com>