swupdate: fix build without json-c

swupdate enables SURICATTA_HAWKBIT by default, which unconditionally selects
JSON. This breaks the build when the optional json-c dependency is not built.
Add a patch fixing SURICATTA_HAWKBIT dependencies.

Fixes:
http://autobuild.buildroot.net/results/e61/e6179f515589a42a9aee16b54b897ef9111e7f4b/
http://autobuild.buildroot.net/results/dba/dba54b00c81f62d957a8c189dde39ba0db8864e6/



Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>