Fix the kernel doc of xbc_get_info() to add '@' to the parameters.

Link: https://lkml.kernel.org/r/163525086738.676803.15352231787913236933.stgit@devnote2

Fixes: e306220c ("bootconfig: Add xbc_get_info() for the node information")
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>