UPSTREAM: northbridge/amd/lx: remove unused function declaration

Remove an unusued function declaration that caused problems while
compiling the target.

BUG=None
BRANCH=None
TEST=None

Signed-off-by: Antonello Dettori <dev@dettori.io>
Reviewed-on: https://review.coreboot.org/16435
Tested-by: build bot (Jenkins)
Reviewed-by: Martin Roth <martinroth@google.com>

Change-Id: Idfd73693e9b0e1777cafa4706113fde394e95795
Reviewed-on: https://chromium-review.googlesource.com/382081
Commit-Ready: Furquan Shaikh <furquan@chromium.org>
Tested-by: Furquan Shaikh <furquan@chromium.org>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

src/northbridge/amd/lx/northbridge.h

@@ -19,7 +19,6 @@
 #include <cpu/amd/lxdef.h>
 
 /* northbridge.c */
-unsigned int lx_scan_root_bus(device_t root, unsigned int max);
 int sizeram(void);
 
 /* northbridgeinit.c */