package/python-avro: don't refer to avro-c version variable
Like for other packages sharing the same version number, we
can't rely on Make variable expansion. It's working by chance
since avro-c is sorted before python-avro by the Buildroot
main Makefile [1].
[1] https://git.buildroot.net/buildroot/tree/Makefile?h=2022.02.1#n533
Signed-off-by: Romain Naour <romain.naour@gmail.com>
Cc: Titouan Christophe <titouanchristophe@gmail.com>
[yann.morin.1998@free.fr: duplicate comment]
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>