shared: make scratchbuf_str static

It fixes linking problem

tools/depmod.o: In function `output_symbols_bin':
depmod.c:(.text.output_symbols_bin+0x135): undefined reference to `scratchbuf_str'

for -O0 build, where gcc doesn't actually inline it.

Signed-off-by: Yauheni Kaliuta <yauheni.kaliuta@redhat.com>
diff --git a/shared/scratchbuf.h b/shared/scratchbuf.h
index c12e490..27ea9d9 100644
--- a/shared/scratchbuf.h
+++ b/shared/scratchbuf.h
@@ -19,7 +19,7 @@
 void scratchbuf_release(struct scratchbuf *buf);
 
 /* Return a C string */
-inline char *scratchbuf_str(struct scratchbuf *buf)
+static inline char *scratchbuf_str(struct scratchbuf *buf)
 {
 	return buf->bytes;
 }