Change the log level from error to warn

This log is said to be ignored so it should not
be at the level of an error as that could confuse
people.

Test: N/A
Change-Id: I561fc8c16337de9d40714d87d3525f432f5afad7
diff --git a/keystore2/src/operation.rs b/keystore2/src/operation.rs
index eabc1ab..11eaf17 100644
--- a/keystore2/src/operation.rs
+++ b/keystore2/src/operation.rs
@@ -290,7 +290,7 @@
 
         // We abort the operation. If there was an error we log it but ignore it.
         if let Err(e) = map_km_error(self.km_op.abort()) {
-            log::error!("In prune: KeyMint::abort failed with {:?}.", e);
+            log::warn!("In prune: KeyMint::abort failed with {:?}.", e);
         }
 
         Ok(())