btrfs-progs: build, fix version macro name

Autoconf changed it to PACKAGE_VERSION and moved to config.h.

Signed-off-by: David Sterba <dsterba@suse.cz>
diff --git a/Documentation/Makefile.in b/Documentation/Makefile.in
index 5ae1fca..1f83685 100644
--- a/Documentation/Makefile.in
+++ b/Documentation/Makefile.in
@@ -58,8 +58,8 @@
 RM = @RM@
 RMDIR = @RMDIR@
 LN_S = @LN_S@
-BTRFS_VERSION = $(shell sed -n 's/.*BTRFS_BUILD_VERSION "Btrfs \(.*\)"/\1/p'\
-		  ../version.h)
+BTRFS_VERSION = $(shell sed -n 's/.*PACKAGE_VERSION "\(.*\)"/\1/p'\
+		  ../config.h)
 
 ifneq ($(findstring $(MAKEFLAGS),s),s)
 ifndef V