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>

package/avro-c/avro-c.mk

@@ -4,6 +4,7 @@
 #
 ################################################################################
 
+# When updating the version, please also update python-avro
 AVRO_C_VERSION = 1.11.0
 AVRO_C_SITE = https://www-eu.apache.org/dist/avro/avro-$(AVRO_C_VERSION)/c
 AVRO_C_LICENSE = Apache-2.0

package/python-avro/python-avro.mk

@@ -4,7 +4,8 @@
 #
 ################################################################################
 
-PYTHON_AVRO_VERSION = $(AVRO_C_VERSION)
+# When updating the version, please also update python-avro
+PYTHON_AVRO_VERSION = 1.11.0
 PYTHON_AVRO_SITE = \
 	https://www-eu.apache.org/dist/avro/avro-$(PYTHON_AVRO_VERSION)/py
 PYTHON_AVRO_SOURCE = avro-$(PYTHON_AVRO_VERSION).tar.gz