media: uvcvideo: Increase number of URBs for UVC

[6by9]

Speculative for https://forums.raspberrypi.com/viewtopic.php?t=371104 based on a past experience with "fast" USB3 UVC devices on "slow" processors, and running out of URBs resulting in dropped image data.

[P33M]

From the lsusb dump in the thread, these are apparently FS devices:

	Line 62:    Port 1: 0000.02a0 5Gbps power Rx.Detect
	Line 733:    Port 1: 0000.0303 lowspeed power enable connect
	Line 734:    Port 2: 0000.0103 power enable connect
	Line 799:    Port 1: 0000.02a0 5Gbps power Rx.Detect
	Line 940:    Port 1: 0000.0100 power
	Line 941:    Port 2: 0000.0103 power enable connect

Bus 3 device 3 could be either of the Port 2 connections.

[6by9]

I couldn't find that detail, hence the suggestion.
It sounds unlikely though, so I'll close this (CI will still complete).