package/skalibs: fix build with xtensa

package/skalibs: fix build with xtensa

Build with xtensa toolchain is broken since bump to version 2.10.0.2 in
commit 4d5587cb56224b2b28f53b0202fb14b2ab32d5fb indeed patch was dropped
assuming that it was included upstream but this assumption was wrong.

The code was just reworked in version 2.10.0.0 and commit
https://github.com/skarnet/skalibs/commit/21e6ea800cc96ba76e94ad8de1dfa58ab1b7ceb6

Fixes:
 - http://autobuild.buildroot.org/results/ee58ffa7b2f0be46ef7bc0ba38d3142f26a9bce9

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