Compiler warnings

Greetings,

Not sure if anyone else has been seeing these, but I'm getting a bit
tired of them. Neither is a live bug, but they also seem pretty simple
to fix. The attached patch makes both of these warnings go away. At
least for my common build, these are the only warnings that are thrown.

I'm building with:

gcc (Ubuntu 5.4.0-6ubuntu1~16.04.4) 5.4.0 20160609

.../src/backend/storage/lmgr/lwlock.c: In function ‘LWLockRelease’:
.../src/backend/storage/lmgr/lwlock.c:1802:5: warning: ‘mode’ may be used uninitialized in this function [-Wmaybe-uninitialized]
if (mode == LW_EXCLUSIVE)
^
.../src/backend/utils/cache/plancache.c: In function ‘GetCachedPlan’:
.../src/backend/utils/cache/plancache.c:1232:9: warning: ‘plan’ may be used uninitialized in this function [-Wmaybe-uninitialized]
return plan;
^

Thoughts?

Thanks!

Stephen