bc: simpler calling convention for bc_read_file(), bc_program_search()

bc: simpler calling convention for bc_read_file(), bc_program_search()

function                                             old     new   delta
bc_vm_run                                           1854    2020    +166
bc_program_assign                                    482     476      -6
bc_program_pushVar                                   225     215     -10
bc_program_call                                      366     356     -10
bc_program_num                                      1126    1115     -11
bc_program_copyToVar                                 354     343     -11
bc_program_search                                    164     152     -12
bc_program_execStr                                   573     559     -14
bc_program_exec                                     4544    4530     -14
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 1/8 up/down: 166/-88)            Total: 78 bytes
   text	   data	    bss	    dec	    hex	filename
 988523	    485	   7296	 996304	  f33d0	busybox_old
 988601	    485	   7296	 996382	  f341e	busybox_unstripped

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