ALSA: sb: Minor coding style fixes

ALSA: sb: Minor coding style fixes

The handling of snd_ctl_new1() and snd_ctl_add() can be sometimes
tricky, as snd_ctl_add() automatically removes the passed object at
its error path.  The recent fix addressed an overlooked issue that is
relevant with that in SB driver code, and it can be a bit more
simplified by assigning to a temporary variable, i.e. storing to the
struct field only after the creation succeeds.

Link: https://lore.kernel.org/r/20210608140540.17885-3-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>