Sync libnfc.pc includedir with the rest of the project source files.

When I introduced headers separation (aka includes-revamp branch), the libnfc source code includes have been changed from '#include "../xx/nfc*.h"' to '#include <nfc/nfc*>' (when compiling, the source include dir (src/include) has precedence over '${prefix}/include').  For the sake of consistency, update libnfc.pc includedir so that compiling third party code using '#include <nfc/nfc*>' just works (tm).  This provides much more consistent headers since they are usually referred relative to the includedir (exceptions are e.g. glib, gtk, xorg... quite bigger than libnfc I could say).

libnfc.pc.in

@@ -1,7 +1,8 @@
 prefix=@prefix@
 exec_prefix=@exec_prefix@
 libdir=@libdir@
-includedir=@includedir@/nfc
+includedir=@includedir@
+
 Name: libnfc
 Description: Near Field Communication (NFC) library
 Version: @VERSION@