installer: fix incremental builds

Building "sof" does not rebuild the .ri firmware file. Switch to the
"bin" target which is what ./scripts/xtensa-build-all.sh builds.

Fixes: 4798096 ("installer: (re)build firmware, topologies and user
space tools)

Signed-off-by: Marc Herbert <marc.herbert@intel.com>
(cherry picked from commit 21f4e74)

Author: marc-hb

installer/GNUmakefile

@@ -157,7 +157,7 @@ endif
 ${BUILD_SOF_RIS}: ${BUILDS_ROOT}/build_%_${TOOLCHAIN}/sof.ri: | ${BUILDS_ROOT}
 	cd ${BUILDS_ROOT} && bdir="$$(dirname $@)" &&  \
       if [ -d $${bdir} ] && [ xcc != "${TOOLCHAIN}" ] ; then \
-        cmake --build $${bdir} -- sof; else \
+        cmake --build $${bdir} -- bin; else \
       $(CURDIR)/../scripts/xtensa-build-all.sh $*; fi