apex: add errno reporting for mount

Change-Id: Ic6db027b5b898332bf2c86c714adabb73acc7b1e
diff --git a/twrpApex.cpp b/twrpApex.cpp
index d9505c3..a6041f1 100755
--- a/twrpApex.cpp
+++ b/twrpApex.cpp
@@ -138,7 +138,7 @@
 
 	ret = mount(loop_device.c_str(), bind_mount.c_str(), "ext4", MS_RDONLY, nullptr);
 	if (ret != 0) {
-		LOGERR("unable to mount loop device %s to %s\n", loop_device.c_str(), bind_mount.c_str());
+		LOGERR("unable to mount loop device %s to %s. reason: %s\n", loop_device.c_str(), bind_mount.c_str(), strerror(errno));
 		return false;
 	}