package/iwd: fix build with uclibc-ng

package/iwd: fix build with uclibc-ng

Fix the following build failure with uclibc-ng raised since bump to
version 1.17 in commit 9badccc9d4887aa2365d7350e3b26bd4250dad48:

/home/giuliobenetti/autobuild/run/instance-3/output-1/host/lib/gcc/xtensa-buildroot-linux-uclibc/10.3.0/../../../../xtensa-buildroot-linux-uclibc/bin/ld: src/sae.o: in function `sae_rx_authenticate':
sae.c:(.text+0xd74): undefined reference to `reallocarray'

Fixes:
 - http://autobuild.buildroot.org/results/c6d3f86282c44645b4f1c61882dc63ccfc8eb35a

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Reviewed-by: Peter Seiderer <ps.report@gmx.net>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>