software/grafana: backport a loki fix for golang 1.16

for https://github.com/grafana/loki/issues/3177

While investingating this, I realized loki officially supports golang 1.15, but
beside this, everything seems to work fine, so let's keep using 1.16

software/grafana/software.cfg

@@ -40,8 +40,8 @@ revision      = v7.5.2-0-gca413c612f
 [go_github.com_grafana_loki]
 <= go-git-package
 go.importpath = github.com/grafana/loki
-repository    = https://github.com/grafana/loki
-revision      = v2.2.1-0-gbabea82e
+repository    = https://github.com/perrinjerome/loki
+revision      = v2.2.1-1-gda6d45f2
 
 [go_github.com_influxdata_influxdb]
 <= go-git-package