base: syslog: fix error log case
base: syslog: fix error log case

Previously, err_buf would just be a slice of 1024 zero bytes, but it
seems like we wanted to print out the warning message instead.

BUG=None
TEST=tools/presubmit

Change-Id: I92613fd4b9e09b951cd52f5a1ab227068e9de092
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosvm/+/3617366
Commit-Queue: Daniel Verkamp <72bc170b46ec491f7bdd4359a1c0bfed274de40c@chromium.org>
Tested-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
Reviewed-by: Anton Romanov <7c8c28e1283c1d87f2c3df4d6b5c74b6ae02bcd9@google.com>
Reviewed-by: Vikram Auradkar <50abc1d85bedfd527fc7dee23f4819d1f0d946ec@google.com>

google/crosvm,google/crosvm,google/crosvm,google/crosvm