lmbench: fix doc install failure

Fix the failure:
cp: cannot create regular file `/usr/share/man/man1/bargraph.1': Permission denied
mkdir: cannot create directory `/usr/share/man/man9': Permission denied

Signed-off-by: Jackie Huang <jackie.huang@windriver.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>