Portability improvement

Makefile.inc uses $( ) syntax on the shell. That's isn't as universal
as one would like.

Change-Id: I9a8fd511eef7fefc1458d5bae2cd7ef5475b7392
Signed-off-by: Patrick Georgi <patrick@georgi-clan.de>
Reviewed-on: http://review.coreboot.org/777
Tested-by: build bot (Jenkins)
Reviewed-by: Bernhard Urban <lewurm@gmail.com>

Makefile.inc

@@ -225,7 +225,7 @@ lint lint-stable:
 		grep "^# DESCR:" $$script | sed "s,.*DESCR: *,," ; \
 		echo ========; \
 		$$script > $$LINTLOG; \
-		if [ `echo $$( wc -l $$LINTLOG ) | cut -d' ' -f1` -eq 0 ]; then \
+		if [ `cat $$LINTLOG | wc -l` -eq 0 ]; then \
 			printf "success\n\n"; \
 		else \
 			echo test failed: ; \