openssl: fix c_rehash dumbness

The new c_rehash from openssl 1.0.2 can't take a minus in the directory
string since the regex for matching commands checks for - in any
position instead of just the beginning to trigger the command parser. Fixes:
http://autobuild.buildroot.net/results/ee6/ee683569350d5deaf0ccc603ed7066bffb83cbe3/



Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>