mainloop: Make HwmonIO injectable dependency

HwmonIO was make into a interface object implementation.  This patch
transitions mainloop to receive a pointer to this interface to allow for
injection testing.

Signed-off-by: Patrick Venture <venture@google.com>
Change-Id: Iaa470fafccb42c4d7fbabac0dc92f96c8075faf2
diff --git a/hwmonio.hpp b/hwmonio.hpp
index f0c7248..b0b8617 100644
--- a/hwmonio.hpp
+++ b/hwmonio.hpp
@@ -109,6 +109,7 @@
   private:
     std::string _p;
 };
+
 } // namespace hwmonio
 
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