move getEnv methods into env namespace

Move the getEnv(...) methods into the env namespace,
for consistency.

Change-Id: I4055d9456c17f8b20071cdee1b8e531c10fb0c7e
Signed-off-by: Patrick Venture <venture@google.com>
diff --git a/fan_speed.cpp b/fan_speed.cpp
index 2652f8d..15ce946 100644
--- a/fan_speed.cpp
+++ b/fan_speed.cpp
@@ -58,7 +58,7 @@
 
 void FanSpeed::enable()
 {
-    auto enable = getEnv("ENABLE", type, id);
+    auto enable = env::getEnv("ENABLE", type, id);
     if (!enable.empty())
     {
         auto val = std::stoul(enable);