fs_mgr_avb: fix return value check of fs_mgr_get_boot_config()

fs_mgr_get_boot_config() returns true/false but the return value check
in current fs_mgr_avb is for 0/1. This was introduced during a refactoring.

Check true/false for the return value.

Bug: 33254008
Test: manual test AVB on bullhead
Change-Id: I72c366627214df4a99c4d9cf1eb577e94f7afb31
diff --git a/fs_mgr/fs_mgr_avb.cpp b/fs_mgr/fs_mgr_avb.cpp
index 35577e3..a762038 100644
--- a/fs_mgr/fs_mgr_avb.cpp
+++ b/fs_mgr/fs_mgr_avb.cpp
@@ -454,12 +454,12 @@
     // be returned when there is an error.
 
     std::string hash_alg;
-    if (fs_mgr_get_boot_config("vbmeta.hash_alg", &hash_alg) == 0) {
-        if (hash_alg == "sha256" || hash_alg == "sha512") {
-            return true;
-        }
+    if (!fs_mgr_get_boot_config("vbmeta.hash_alg", &hash_alg)) {
+        return false;
     }
-
+    if (hash_alg == "sha256" || hash_alg == "sha512") {
+        return true;
+    }
     return false;
 }