pstore: Fix memory leak when decompress using big_oops_buf

After sucessful decompressing, the buffer which pointed by 'buf' will be
lost as 'buf' is overwrite by 'big_oops_buf' and will never be freed.

Signed-off-by: Liu ShuoX <shuox.liu@intel.com>
Acked-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Tony Luck <tony.luck@intel.com>

fs/pstore/platform.c

@@ -497,6 +497,7 @@ void pstore_get_records(int quiet)
 							big_oops_buf_sz);
 
 			if (unzipped_len > 0) {
+				kfree(buf);
 				buf = big_oops_buf;
 				size = unzipped_len;
 				compressed = false;