cbfstool: initialize offset field in buffer_init()

If one wants to use buffer_init() for initializing a
struct buffer all the fields should be initialized.

Change-Id: I791c90a406301d662fd333c5b65b2e35c934d0f7
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: http://review.coreboot.org/12172
Tested-by: build bot (Jenkins)
Reviewed-by: Martin Roth <martinroth@google.com>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Patrick Georgi <pgeorgi@google.com>

util/cbfstool/common.h

@@ -81,6 +81,7 @@ static inline void buffer_init(struct buffer *b, char *name, void *data,
 	b->name = name;
 	b->data = data;
 	b->size = size;
+	b->offset = 0;
 }
 
 /* Splice a buffer into another buffer. Note that it's up to the caller to