abuf: Allow incrementing the size

Provide a convenience function to increment the size of the abuf.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/lib/abuf.c b/lib/abuf.c
index bd27046..ce2cff5 100644
--- a/lib/abuf.c
+++ b/lib/abuf.c
@@ -82,6 +82,11 @@
 	}
 }
 
+bool abuf_realloc_inc(struct abuf *abuf, size_t inc)
+{
+	return abuf_realloc(abuf, abuf->size + inc);
+}
+
 void *abuf_uninit_move(struct abuf *abuf, size_t *sizep)
 {
 	void *ptr;