hush: use ash's read builtin

function                                             old     new   delta
shell_builtin_read                                     -    1000   +1000
set_local_var_from_halves                              -      24     +24
setvar2                                                -       7      +7
...
popstring                                            140     134      -6
ash_main                                            1375    1368      -7
setvar                                               184     174     -10
arith_set_local_var                                   36       -     -36
builtin_read                                        1096     185    -911
------------------------------------------------------------------------------
(add/remove: 3/1 grow/shrink: 5/23 up/down: 1038/-1007)        Total: 31 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/shell/builtin_read.h b/shell/builtin_read.h
index 930d014..bc23dc5 100644
--- a/shell/builtin_read.h
+++ b/shell/builtin_read.h
@@ -27,7 +27,7 @@
 };
 
 const char* FAST_FUNC
-builtin_read(void (*setvar)(const char *name, const char *val, int flags),
+shell_builtin_read(void FAST_FUNC (*setvar)(const char *name, const char *val),
 	char       **argv,
 	const char *ifs,
 	int        read_flags,