zfs-dkms: fix shell-init error message

If all zfs dkms modules have been removed, a shell-init error message
may appear, because /var/lib/dkms/zfs does no longer exist.
Resolve this by leaving the directory earlier on.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Mart Frauenlob <AllKind@fastest.cc>
Closes openzfs#15576

rpm/generic/zfs-dkms.spec.in

@@ -103,6 +103,7 @@ if [ -d ${dkms_root}/%{module} ]; then
             fi
         fi
     done
+    cd ${dkms_root}
 fi
 
 # Uninstall this version of zfs dkms modules before installation of the package.