Boot: Exit from loop when TLV has been found

In order to shorten the execution time exit from the
TLV look-up loop when matching TLV has been found.

Change-Id: Iacaca39f95411c808a8b520291a7c3f51c98193e
Signed-off-by: Tamas Ban <tamas.ban@arm.com>
diff --git a/bl2/ext/mcuboot/bootutil/src/image_validate.c b/bl2/ext/mcuboot/bootutil/src/image_validate.c
index d471155..e62455c 100644
--- a/bl2/ext/mcuboot/bootutil/src/image_validate.c
+++ b/bl2/ext/mcuboot/bootutil/src/image_validate.c
@@ -235,6 +235,7 @@
             }
 
             sha256_valid = 1;
+            break;
         }
 
         /* Avoid integer overflow. */