Use POSIX-compatible redirection in riscv-tools Makefile

The Makefile currently uses &> which works in bash, but not other
shells. On Ubuntu 20.04.6 LTS, `make` uses /bin/sh, which is a symlink
to dash. dash does not support this syntax.

This PR replaces &> with > and 2>&1, which is compatible with both bash
and dash.

software/riscv-tools/Makefile

@@ -100,9 +100,9 @@ define patch_if_new
 	for p in ${$@_patch}; \
 	do \
 		echo "Checking if ${$@_base_patch} is applied..."; \
-		cd ${$@_src_root}; $(CHECK_PATCH) $$p &> /dev/null && continue; \
+		cd ${$@_src_root}; $(CHECK_PATCH) $$p > /dev/null 2>&1 && continue; \
 		echo "Applying unapplied patch to ${$@_src_root};" \
-		cd ${$@_src_root}; $(APPLY_PATCH) $$p &> /dev/null && continue; \
+		cd ${$@_src_root}; $(APPLY_PATCH) $$p > /dev/null 2>&1 && continue; \
 	done
 endef