sys_ioctl: truncate 'cmd' from 'unsigned long' to 'unsigned int'

Kernel receive arguments for syscall as if they have type '[unsigned] long',
but signature of 'sys_ioctl' is

   long sys_ioctl(unsigned int fd, unsigned int cmd, unsigned long arg);

So cmd is truncated to 'unsigned int' in kernel. Therefore
ioctl(15, 0xffffffffc008551a, 0x1041bf0) and
ioctl(15, 0x00000000c008551a, 0x1041bf0) are the same ioctls.

Valgrind should truncate 'cmd' argument too.
sys_ioctl: implement a few SNDDRV_CTL_* ioctls