contrib: qt: Fix shasum check filelist format

This kind of error occurred on darwin when shasum check attempt wat made on Qt contribs :
```
+ make fetch
grep -- " qtdeclarative-everywhere-src-5.15.1.tar.xz$" "../src/qtdeclarative/SHA512SUMS" && (cd ../tarballs && shasum -a 512 --check /dev/stdin) < "../src/qtdeclarative/SHA512SUMS"
193ec706b764330a2ae00614b13482b7586642f9cfd32458e8c975daa07ba25f0f9887de0918c4034f52f613b860677c09c46a3b7d07d4229446cfc0805bcccd qtdeclarative-everywhere-src-5.15.1.tar.xz
shasum: /dev/stdin: no properly formatted SHA checksum lines found
make: *** [.sum-qtdeclarative] Error 1
umxprime@umxprime-m1 ~ % shasum -a 512 /Users/umxprime/code/videolan/vlc/contrib/tarballs/qtdeclarative-everywhere-src-5.15.1.tar.xz
193ec706b764330a2ae00614b13482b7586642f9cfd32458e8c975daa07ba25f0f9887de0918c4034f52f613b860677c09c46a3b7d07d4229446cfc0805bcccd  /Users/umxprime/code/videolan/vlc/contrib/tarballs/qtdeclarative-everywhere-src-5.15.1.tar.xz
umxprime@umxprime-m1 ~ %
```
This was mainly due to a missing whitespace between the sum and the filename in the SHA512SUMS list