hi846 camera hangs

Using Millipixels from this: millipixels!73 (merged), the selfie camera tends to fall into a broken state where Millipixels will show an error, and the kill switch won't help.

Logs captured with dorota.czaplejewicz/libcamera@d54d6f87 but should be the same with any other commit.

LIBGL_DEBUG=verbose MESA_DEBUG=verbose EGL_LOG_LEVEL=debug LIBCAMERA_LOG_LEVELS=DEBUG LD_LIBRARY_PATH=caminstall/lib/aarch64-linux-gnu/ caminstall/bin/cam -c /base/soc@0/bus@30800000/i2c@30a40000/camera@20 -s height=480,width=640 --capture=3 -F'selfiq#.bin'

2:26:03.119751930] [8835] DEBUG BayerPipeline handler.cpp:272 Found entities: [hi846 2-0020|0] -> [0|imx8mq-mipi-csi2 30a70000.csi|1] -> [0|csi|1] -> [0|csi capture]
[2:26:03.121455652] [8835] DEBUG V4L2 v4l2_videodevice.cpp:632 /dev/video0[13:cap]: Opened device platform:30a90000.csi: imx-capture: imx-capture
[2:26:03.122551064] [8835] DEBUG V4L2 v4l2_device.cpp:627 'hi846 2-0020': Control: Exposure (0x00980911)
[...]
[2:26:03.134093098] [8835] DEBUG CameraSensor camera_sensor.cpp:633 'hi846 2-0020': Apply test pattern mode 0
[2:26:03.134569281] [8835] ERROR V4L2 v4l2_subdevice.cpp:575 'hi846 2-0020': Unable to set format on pad 0: Device or resource busy
[2:26:03.134629524] [8835] DEBUG BayerPipeline handler.cpp:577 Media bus code 0x300e not supported for this pipeline
[2:26:03.134669605] [8835] ERROR V4L2 v4l2_subdevice.cpp:575 'hi846 2-0020': Unable to set format on pad 0: Device or resource busy
[2:26:03.134702607] [8835] DEBUG BayerPipeline handler.cpp:577 Media bus code 0x300e not supported for this pipeline
[2:26:03.134736089] [8835] ERROR V4L2 v4l2_subdevice.cpp:575 'hi846 2-0020': Unable to set format on pad 0: Device or resource busy
[2:26:03.134768250] [8835] DEBUG BayerPipeline handler.cpp:577 Media bus code 0x300e not supported for this pipeline
[2:26:03.134819013] [8835] ERROR BayerPipeline handler.cpp:634 No valid configuration found
[2:26:03.134964100] [8835] ERROR BayerPipeline handler.cpp:1498 Failed to initialize pipeline for sensor hi846, skipping
[2:26:03.135977188] [8835] DEBUG V4L2 v4l2_videodevice.cpp:1536 /dev/video0[13:cap]: Releasing buffers
[2:26:03.136079313] [8835] ERROR V4L2 v4l2_videodevice.cpp:1241 /dev/video0[13:cap]: Unable to request 0 buffers: Device or resource busy