mailmap: Fix text encoding for Niklas Söderlund

There are commits that mess up the encoding of 'ö' in Söderlund, add a
correct entry to .mailmap.

Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Link: https://lore.kernel.org/r/20211014212906.2331293-1-niklas.soderlund+renesas@ragnatech.se


Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>