[BUGFIX] Responsive sourceCollection width not usable out of the box

The dimension settings in the source collections was overriden after
calculation. Now the result will not be overriden anymore.

Resolves: #53169
Releases: 6.2
Change-Id: I34b4dbab5e99b5cf3d790f92d06d11d31b9b8140
Reviewed-on: https://review.typo3.org/25077
Reviewed-by: Ingo Schmitt
Tested-by: Ingo Schmitt
Reviewed-by: Sebastian Fischer
Tested-by: Sebastian Fischer
Reviewed-by: Markus Klein
Tested-by: Markus Klein