tools/libs/stat: fix broken build

tools/libs/stat: fix broken build

Making getBridge() static triggered a build error with some gcc versions:

error: 'strncpy' output may be truncated copying 15 bytes from a string of
length 255 [-Werror=stringop-truncation]

Fix that by using a buffer with 256 bytes instead.

Fixes: 6d0ec053907794 ("tools: split libxenstat into new tools/libs/stat directory")
Signed-off-by: Juergen Gross <jgross@suse.com>
Acked-by: Wei Liu <wl@xen.org>
(cherry picked from commit c8099e48c3dbb8c7399551a265756ecf354eece2)