cifs-utils: disable man page generation

Buildroot does not generate documentation for target.

This fixes the build on hosts where the rst2man command does not support
the --syntax-highlight parameter.

Fixes:
http://autobuild.buildroot.net/results/265/2655c0e1fa3ad0a10b4aed39a17feead94e47bfb/
http://autobuild.buildroot.net/results/92d/92d7c608f717bbfe01ecfb9bc9604cb303d8594c/
http://autobuild.buildroot.net/results/4b9/4b95404a89a595ca9c1e3df912169e9d36ff2bd7/

Cc: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
(cherry picked from commit 57d16fd480d3eb57822e634e409fb0bbc4dd475b)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/cifs-utils/cifs-utils.mk

@@ -15,7 +15,7 @@ CIFS_UTILS_DEPENDENCIES = host-pkgconf
 
 # Let's disable PIE unconditionally. We want PIE to be enabled only by
 # the global BR2_RELRO_FULL option.
-CIFS_UTILS_CONF_OPTS = --disable-pie
+CIFS_UTILS_CONF_OPTS = --disable-pie --disable-man
 
 ifeq ($(BR2_PACKAGE_KEYUTILS),y)
 CIFS_UTILS_DEPENDENCIES += keyutils