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

Makefile

@@ -981,7 +981,7 @@ _modinst_:
 # boot a modules.dep even before / is mounted read-write.  However the
 # boot script depmod is the master version.
 PHONY += _modinst_post
-_modinst_post: _modinst_
+_modinst_post: include/config/kernel.release _modinst_
 	$(Q)$(MAKE) -f $(srctree)/scripts/Makefile.fwinst obj=firmware __fw_modinst
 	$(call cmd,depmod)