Correct shellcheck make recipe

Consolidated the shellcheck call in the
make recipe down to a single call of
shellcheck. Corrected script errors that
have been skipped. Corrected script errors
that have been introduced because make
wasn't reporting any errors from shellcheck.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Giuseppe Di Natale <dinatale2@llnl.gov>
Closes #5976

Makefile.am

@@ -52,17 +52,13 @@ cstyle:
 
 shellcheck:
 	@if type shellcheck > /dev/null 2>&1; then \
-		shellcheck --exclude=SC1090 --format gcc scripts/paxcheck.sh \
+		shellcheck --exclude=SC1090 --format=gcc scripts/paxcheck.sh \
 			scripts/zloop.sh \
 			scripts/zfs-tests.sh \
 			scripts/zfs.sh \
-			scripts/commitcheck.sh; \
-		(find cmd/zed/zed.d/*.sh -type f) | \
-		 grep -v 'zfs-script-config' | \
-		 while read file; do \
-			shellcheck --exclude=SC1090 --format gcc "$$file"; \
-		 done; \
-	 fi
+			scripts/commitcheck.sh \
+			$$(find cmd/zed/zed.d/*.sh -type f); \
+	fi
 
 lint: cppcheck paxcheck