scripts/run-regression-tests: Fix the build against Linux kernel v5.10

From the Linux kernel help text:

  modules_prepare - Set up for building external modules


git-svn-id: http://svn.code.sf.net/p/scst/svn/trunk@9217 d57e44dd-8a1f-0410-8b47-8ef2f437770f

scripts/run-regression-tests

@@ -379,7 +379,7 @@ function compile_kernel {
 
   echo "Compiling the patched kernel ..."
   if (cd "${outputdir}/linux-$k" \
-      && make -s prepare \
+      && make -s modules_prepare \
       && make -s scripts \
       && for subdir; do LC_ALL=C make -k M="${subdir}"; done
      ) &> "${outputfile}"