Makefile: Fix install error with make -j option

Make modules_install fails with -j option:

   DEPMOD
 Usage: .../.source/linux/scripts/depmod.sh /sbin/depmod <kernelrelease>
 make[1]: *** [_modinst_post] Error 1

Adding kernelrelease dependency to fix this.

Signed-off-by: Robert Richter <robert.richter@calxeda.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Michal Marek <mmarek@suse.cz>