Update VeUnoDaoYieldDistributor.sol: Usage of 'internal' function for modifier

[0xScratch]

Here, the internal function used for modifier 'onlyByOwnGov' do saves some gas.

These links will help:

• https://gist.github.com/grGred/9bab8b9bad0cd42fc23d4e31e7347144#use-internal-view-functions-in-modifiers-to-save-bytecode
• https://www.rareskills.io/post/gas-optimization#viewer-527f6
• Seems to be a worthy discussion -- https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3347/

Thanks!