src/include: Doxygen fixes

- Join doxygen file command with the file description
- Give extended file location so doxygen knows which early_sbmus.h
the file is.  (I don't get this either, but it fixes the warning)

Change-Id: Ia91fb1ac1e9687e1a5a5cb5234696b3c24d4cd24
Signed-off-by: Martin Roth <gaumless@gmail.com>
Reviewed-on: http://review.coreboot.org/8174
Tested-by: build bot (Jenkins)
Reviewed-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
diff --git a/src/include/device/early_smbus.h b/src/include/device/early_smbus.h
index 5e15bb1..437a569 100644
--- a/src/include/device/early_smbus.h
+++ b/src/include/device/early_smbus.h
@@ -18,7 +18,7 @@
  */
 
 /**
- * @file early_smbus.h
+ * @file device/early_smbus.h
  *
  * This file defines a common API for accessing the SMBus during early
  * initialization. It defines the prototypes for common SMBus functions. The