setserial: don't build setserial.cat

Fixes http://autobuild.buildroot.net/results/c73/c736933d4110865008f2d1e8b531b6e392c68285/

Don't use 'make all', as that also builds setserial.cat which needs nroff on
the build machine (and isn't needed anyway as it doesn't get installed /
referenced from anywhere).

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/setserial/setserial.mk

@@ -10,6 +10,8 @@ SETSERIAL_SOURCE = setserial_$(SETSERIAL_VERSION).orig.tar.gz
 SETSERIAL_SITE = http://snapshot.debian.org/archive/debian/20131001T214925Z/pool/main/s/setserial
 SETSERIAL_LICENSE = GPLv2
 SETSERIAL_LICENSE_FILES = debian/copyright
+# make all also builds setserial.cat which needs nroff
+SETSERIAL_MAKE_OPT = setserial
 
 define SETSERIAL_APPLY_DEBIAN_PATCHES
 	# Touching gorhack.h is needed for the Debian patch 18 to work