sound: oss: uart401: remove unneeded NULL check

"devc" can't be NULL here so there is no need to check.  Also I removed
the "devc = NULL" assignment because devc is stored on stack so it's
a no-op.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>