Fix a couple of pedantic warnings
This addresses the following type warnings emitted by clang:
1) src/watch.c:192:2: warning: void function 'watch_apply' should not return void expression [-Wpedantic]
return watch_apply_changes(source, WATCH_EVENT_LOAD, changed);
^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2) include/tig/keys.h:57:6: warning: ISO C forbids forward references to 'enum' types [-Wpedantic]
enum status_code get_key_value(const char **name, struct key *key);
^
The warnings was emitted when executing the following command:
> make clean all CFLAGS="-Wpedantic -Wno-extra-semi -Wno-variadic-macros -Wno-gnu-empty-initializer"