libbb: consolidate the code to set termios unbuffered mode

function                                             old     new   delta
set_termios_to_raw                                     -     116    +116
count_lines                                           72      74      +2
powertop_main                                       1458    1430     -28
top_main                                             943     914     -29
more_main                                            759     714     -45
fsck_minix_main                                     2969    2921     -48
conspy_main                                         1197    1135     -62
rawmode                                               99      36     -63
------------------------------------------------------------------------------
(add/remove: 1/0 grow/shrink: 1/6 up/down: 118/-275)         Total: -157 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/util-linux/fsck_minix.c b/util-linux/fsck_minix.c
index 0eaac17..2ab7530 100644
--- a/util-linux/fsck_minix.c
+++ b/util-linux/fsck_minix.c
@@ -1226,7 +1226,6 @@
 int fsck_minix_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 int fsck_minix_main(int argc UNUSED_PARAM, char **argv)
 {
-	struct termios tmp;
 	int retcode = 0;
 
 	xfunc_error_retval = 8;
@@ -1271,10 +1270,7 @@
 	read_tables();
 
 	if (OPT_manual) {
-		tcgetattr(0, &sv_termios);
-		tmp = sv_termios;
-		tmp.c_lflag &= ~(ICANON | ECHO);
-		tcsetattr_stdin_TCSANOW(&tmp);
+		set_termios_to_raw(STDIN_FILENO, &sv_termios, 0);
 		termios_set = 1;
 	}