fs: Fix one kernel-doc comment

Fix one kernel-doc comment to silence the warning:

fs/read_write.c:88: warning: Function parameter or member 'maxsize' not described in 'generic_file_llseek_size'

Signed-off-by: Yang Li <yang.lee@linux.alibaba.com>
Reviewed-by: Randy Dunlap <rdunlap@infradead.org>
Message-Id: <20230811014359.4960-1-yang.lee@linux.alibaba.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>