bootconfig: init: Fix memblock leak in xbc_make_cmdline()

bootconfig: init: Fix memblock leak in xbc_make_cmdline()

commit 1ae43851b18afe861120ebd7c426dc44f06bb2bd upstream.

Free unused memblock in a error case to fix memblock leak
in xbc_make_cmdline().

Link: https://lkml.kernel.org/r/163177339181.682366.8713781325929549256.stgit@devnote2
Fixes: 51887d03aca1 ("bootconfig: init: Allow admin to use bootconfig for kernel command line")
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>