psvr2: initialize fallback distortion rotation scales

[DMJC]

Motivation

• Older PSVR2 firmware path left the per-eye rotation/tilt basis terms unset which caused the distortion transform basis (k3/k4) to be zero and could collapse UV sampling and make one eye render incorrectly compared to the other.

Description

• When calibration_block.version_unk < 4, initialize hmd->distortion_calibration[4] and hmd->distortion_calibration[6] to 1.0f so the rotation/tilt scale is the identity for both eyes.
• The existing memset leaves the sine (tilt) terms at zero, so this change produces an identity rotation (cos = 1, sin = 0) for fallback cases.
• This ensures psvr2_compute_distortion_asymmetric receives valid k3/k4 values and prevents UV collapse around the lens center.

Testing

• Reviewed the distortion code paths in psvr2_setup_distortion_and_fovs and psvr2_compute_distortion_asymmetric by source inspection and confirmed the new values flow into the distortion computation (inspection succeeded).
• Attempted to enumerate build targets with ninja -C build -t targets but the command failed due to a missing build/build.ninja in the workspace (build-target enumeration failed).
• No automated unit or integration tests were available or executed in this environment.

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Codex Task