bugfix: build: check for blobs header properly

Check for specific blobs header instead of the folder.

Originally:
checking blobs-ipmid usability... no
checking blobs-ipmid presence... no
checking for blobs-ipmid... no

Now:
checking blobs-ipmid/blobs.hpp usability... yes
checking blobs-ipmid/blobs.hpp presence... yes
checking for blobs-ipmid/blobs.hpp... yes

The bug was that the failure action was placed into the parameter for
the success action.  Therefore, when before it was failing to find it,
it was happy to continue when it should have thrown a configure script
error.

Signed-off-by: Patrick Venture <venture@google.com>
Change-Id: Ib1da487a501c490365b6f66f1ddafb1ed5107eb1
diff --git a/configure.ac b/configure.ac
index 45380fd..7e6da45 100644
--- a/configure.ac
+++ b/configure.ac
@@ -68,7 +68,8 @@
     [AC_MSG_ERROR([Could not find libpci... pciutils package required])]
 )
 AC_CHECK_HEADER(
-    [blobs-ipmid],
+    [blobs-ipmid/blobs.hpp],
+    [],
     [AC_MSG_ERROR(["phosphor-ipmi-blobs required and not found."])]
 )
 AX_PTHREAD([], [AC_MSG_ERROR(["pthread required and not found"])])