init/main.c: Remove redundant space from saved_command_line

There is a space at the end of extra_init_args. In the current logic,
copying extra_init_args to saved_command_line will cause extra spaces
in saved_command_line here or there. Remove the trailing space from
extra_init_args to make the string in saved_command_line look more perfect.

Link: https://lore.kernel.org/all/20240412032950.12687-1-ytcoode@gmail.com/

Signed-off-by: Yuntao Wang <ytcoode@gmail.com>
Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>