bc: simplify zbc_parse_break_or_continue(), logic is the same

bc: simplify zbc_parse_break_or_continue(), logic is the same

function                                             old     new   delta
zbc_parse_stmt_possibly_auto                        2259    2224     -35
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 0/1 up/down: 0/-35)             Total: -35 bytes
   text	   data	    bss	    dec	    hex	filename
 982218	    485	   7296	 989999	  f1b2f	busybox_old
 982183	    485	   7296	 989964	  f1b0c	busybox_unstripped

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>