bootutil: Fix bug defining slot_usage_t structure

There is a missing semicolon.

Signed-off-by: Carlos Falgueras García <carlos.falgueras@wslw.es>
diff --git a/boot/bootutil/src/loader.c b/boot/bootutil/src/loader.c
index 60f9561..252fb24 100644
--- a/boot/bootutil/src/loader.c
+++ b/boot/bootutil/src/loader.c
@@ -74,7 +74,7 @@
 #endif /* MCUBOOT_RAM_LOAD */
 #ifdef MCUBOOT_DIRECT_XIP_REVERT
     /* Swap status for the active slot */
-    struct boot_swap_state swap_state
+    struct boot_swap_state swap_state;
 #endif /* MCUBOOT_DIRECT_XIP_REVERT */
 };
 #endif