Makefile: use absolute path for TOPDIR

Reported by mr_claus on IRC.

This ensure DL_DIR is always an absolute path, like it was before the
build dir reorganization - Fixes vim (patch) build.

Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

CHANGES

@@ -2,7 +2,7 @@
 
 	Additional fixes and cleanups.
 
-	Updated/fixed packages: alsamixergui, fltk, ncurses
+	Updated/fixed packages: alsamixergui, fltk, ncurses, vim
 
 	Issues resolved (http://bugs.uclibc.org):
 

Makefile

@@ -22,7 +22,8 @@
 # Just run 'make menuconfig', configure stuff, then run 'make'.
 # You shouldn't need to mess with anything beyond this point...
 #--------------------------------------------------------------
-TOPDIR:=.
+# absolute path
+TOPDIR:=$(shell pwd)
 CONFIG_CONFIG_IN=Config.in
 CONFIG_DEFCONFIG=.defconfig
 CONFIG=package/config