coccicheck: emit the contents of cocci patch

Telling the user "you got some error messages" without showing what
the errors are is almost useless in CI environment, as the errors
cannot be examined without downloading build artifacts.

Arrange it to spew out the output when it fails.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

Makefile

diff --git a/Makefile b/Makefile
index 7ca2118..0117d00 100644
--- a/Makefile
+++ b/Makefile
@@ -3521,7 +3521,7 @@
 COCCICHECK_PATCH_MUST_BE_EMPTY_FILES = $(COCCICHECK_PATCHES_INTREE)
 endif
 coccicheck: $(COCCICHECK_PATCH_MUST_BE_EMPTY_FILES)
-	! grep -q ^ $(COCCICHECK_PATCH_MUST_BE_EMPTY_FILES) /dev/null
+	! grep ^ $(COCCICHECK_PATCH_MUST_BE_EMPTY_FILES) /dev/null
 
 # See contrib/coccinelle/README
 coccicheck-pending: coccicheck-test