package/v4l2loopback: bump to version 0.12.2 to fix Linux 5.1 compat

This fixes a kernel 5.1.x compatibility issue. The only changes
between 0.12.1 and 0.12.2 are:

d3b198ef6f57ca512fb25147c9d85b922fd4651a Released v0.12.2
376c2c28bd7d4470cd92ff646d6087ca70cd9d2e fixed typo
6edc4b164b1f05bee74cb507a4f50776a65ceb73 mentioned support for 5.0.0
0b8feb80fdef9a415d8250bca1790b3ff23e8391 Replace v4l2_get_timestamp with ktime_get_ts(64)
541e3bc7aaf46dc9a21f92c7f527397fce03dfd8 Update README.md

So the only functional change is the actual ktime_get_ts() fix, which
is needed for Linux 5.1 compatibility. Therefore, bumping is pretty
much the same as backporting just this commit.

Signed-off-by: James Hilliard <james.hilliard1@gmail.com>
[Thomas: extend the commit log]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>