cmd: avb: free partition buffer upon verify completion

Doing the same as the unittests for libavb [1].

Allows to run 'avb verify' multiple times which can be useful after a
failure to be able to re-flash the partition and try again.

[1]
https://android.googlesource.com/platform/external/avb/+/refs/tags/android-9.0.0_r37/test/avb_slot_verify_unittest.cc#156

Signed-off-by: Gary Bisson <gary.bisson@boundarydevices.com>
Reviewed-by: Igor Opaniuk <igor.opaniuk@gmail.com>

cmd/avb.c

@@ -316,6 +316,9 @@ int do_avb_verify_part(struct cmd_tbl *cmdtp, int flag,
 		printf("Unknown error occurred\n");
 	}
 
+	if (out_data)
+		avb_slot_verify_data_free(out_data);
+
 	return res;
 }