package/alsa-lib: fix static build

package/alsa-lib: fix static build

Fix the following build failure raised since bump to version 1.2.5.1 in
commit af19131543926879fb6676a3352c63ac0b2038bc:

/home/buildroot/autobuild/run/instance-0/output-1/host/opt/ext-toolchain/bin/../lib/gcc/arm-buildroot-linux-uclibcgnueabi/9.3.0/../../../../arm-buildroot-linux-uclibcgnueabi/bin/ld: ../src/.libs/libasound.a(control_symbols.o):(.data+0x4): undefined reference to `_snd_module_control_empty'

Fixes:
 - http://autobuild.buildroot.org/results/a8fd791ba4c289cc4fc744a8ff9615bacd9558f3

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>