libpostproc: fix S!=B failure

Implement khem's suggestion, ${S}/configure $(EXTRA_OECONF).

NOTE: with or without autotools-brokensep, the following:
| WARNING: QA Issue: ELF binary 'libpostproc.so.52.0.100'
| has relocations in .text

Signed-off-by: Tim Orling <TicoTimo@gmail.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>

meta-oe/recipes-multimedia/libpostproc/libpostproc_git.bb

@@ -42,5 +42,5 @@ EXTRA_OECONF = " \
 "
 
 do_configure() {
-    ./configure ${EXTRA_OECONF}
+    ${S}/configure ${EXTRA_OECONF}
 }