Qualcomm AI Engine Direct - Minor qnn_config fix (#19388)

### Summary
Some older python version seems to interpret the
qnn_config.htp_performance_mode as a list while newer version just treat
it as an enum. To make it compatible on older python version, remove the
comma.

### Test plan
[PLEASE REMOVE] How did you test this PR? Please write down any manual
commands you used and note down tests that you have written if
applicable.

Author: winskuo-quic