build: Add nobase to the nodist_include_HEADERS

Replace nodist_include_HEADERS with nobase_nodist_include_HEADERS
so that the header files retain their directory structure.
Without it, phosphor-logging/elog-errors.hpp for example installs
in usr/include/ instead of usr/include/phosphor-logging/.

Change-Id: Ib2df7d93fd191316f03e4636ee453030d5a318f4
Signed-off-by: Adriana Kobylak <anoo@us.ibm.com>
diff --git a/Makefile.am b/Makefile.am
index 169c235..fe90c2f 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -4,7 +4,7 @@
 	phosphor-logging/elog.hpp \
 	phosphor-logging/elog-errors-HostEvent.hpp
 
-nodist_include_HEADERS = \
+nobase_nodist_include_HEADERS = \
 	phosphor-logging/elog-errors.hpp \
 	xyz/openbmc_project/Logging/Internal/Manager/server.hpp