fpga: bridge: Use sysfs_emit() instead of sprintf()

fpga: bridge: Use sysfs_emit() instead of sprintf()

According to Documentation/filesystems/sysfs.rst, show() functions
should use sysfs_emit() when formatting the value to be returned to user
space.

This keeps consistent usage of sysfs_emit() across the same file.

Signed-off-by: Dinh Nguyen <dinguyen@kernel.org>
[ Yilun: clarify the necessity of the change in changelog ]
Reviewed-by: Xu Yilun <yilun.xu@intel.com>
Link: https://lore.kernel.org/r/20260117043626.2188219-1-dinguyen@kernel.org
Signed-off-by: Xu Yilun <yilun.xu@linux.intel.com>