pcm: return -ENOSYS when ops or fast_ops callback is NULL

pcm: return -ENOSYS when ops or fast_ops callback is NULL

function is allowed to continue until it checks for error variable, as to
not conflict with original implementation flow

for simple functions involving only one line, return error immediately in
case callback is NULL

Signed-off-by: Adam Miartus <amiartus@de.adit-jv.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>