Well...
I tried to install the repository that Pretoriano mentions but it gives an error when trying to install the zip file.
But...
I found on this site issue 1323 information on how to replace the winedive library version and it worked 
Here adapted to LibreElec:
Code
wget https://k.slyguy.xyz/.decryptmodules/widevine/4.10.2252.5-linux-armv7.so --output-document /tmp/libwidevinecdm.so
cp -a /storage/.kodi/cdm/libwidevinecdm.so /tmp/libwidevinecdm.so.bak
install /tmp/libwidevinecdm.so --preserve-timestamps --owner root --group root --mode 0744 /storage/.kodi/cdm/libwidevinecdm.so