libsubcmd: Move va_end() before exit

libsubcmd: Move va_end() before exit

This patch makes a minor adjustment by moving the va_end call before
exit. Since the exit() function terminates the program, any code
after exit(128) (i.e., va_end(params)) is unreachable and thus not
executed. Placing va_end before exit ensures that the va_list is
properly cleaned up.

Signed-off-by: Luo Yifan <luoyifan@cmss.chinamobile.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lore.kernel.org/r/20241111091701.275496-1-luoyifan@cmss.chinamobile.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>