loader: Fixed warning about uninitialized rc variable

Might get past the loop without going in at least once.

Signed-off-by: Erik Johnson <erik.johnson@nimbelink.com>
diff --git a/boot/bootutil/src/loader.c b/boot/bootutil/src/loader.c
index 9d4f054..b64d106 100644
--- a/boot/bootutil/src/loader.c
+++ b/boot/bootutil/src/loader.c
@@ -1205,7 +1205,7 @@
 static int
 boot_verify_dependencies(struct boot_loader_state *state)
 {
-    int rc;
+    int rc = -1;
     uint8_t slot;
 
     BOOT_CURR_IMG(state) = 0;