Use correct dependency in Makefile.am

Depending on a libtool library should be done using the .la name, not on
the object file.

Fixes hard-to-reproduce parallel build failures, like so:
    http://autobuild.buildroot.org/results/aed/aed3690689b60844e3278626da3c3eb75f2a2586/build-end.log

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>

diff -durN sqlite-3081000.orig/Makefile.am sqlite-3081000/Makefile.am
--- sqlite-3081000.orig/Makefile.am	2015-05-07 16:59:22.000000000 +0200
+++ sqlite-3081000/Makefile.am	2015-05-20 23:30:03.878784079 +0200
@@ -7,7 +7,7 @@
 
 bin_PROGRAMS = sqlite3
 sqlite3_SOURCES = shell.c sqlite3.h
-sqlite3_LDADD = sqlite3.$(OBJEXT) @READLINE_LIBS@
+sqlite3_LDADD = libsqlite3.la @READLINE_LIBS@
 
 include_HEADERS = sqlite3.h sqlite3ext.h