sysvinit: reduce number of mkdir calls in inittab

sysvinit: reduce number of mkdir calls in inittab

The default sysvinit inittab does two separate mkdir calls to create
/dev/pts and /dev/shm. Reduce this to call mkdir only once for both
directories.

This removes id "si3" but keeps ids "si4".."si9" intact rather than
renumbering them. This would just increase the turmoil without any
practical effect.

Based on commit e9db8122fb, by Florian La Roche <F.LaRoche@pilz.de>.

Signed-off-by: Carlos Santos <casantos@datacom.com.br>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>