obs-nvenc: Correct max target quality for AV1

[Bleuzen]

Description

AV1 has a max CQ of 63. Before it was set to 51 for all codecs but this is only the max for H264 and HEVC.

Motivation and Context

Show correct settings for the encoder

How Has This Been Tested?

Set target quality to new maximum and started a local recording. Verified that bitrate and visual quality are lower compared to old max value.

Types of changes

• Bug fix (non-breaking change which fixes an issue)

• Tweak (non-breaking change to improve existing functionality)

Checklist:

• My code has been run through clang-format.
• I have read the contributing document.
• My code is not on the master branch.
• The code has been tested.
• All commit messages are properly formatted and commits squashed where appropriate.
• I have included updates to all appropriate documentation.