V4L/DVB (9193): stk-webcam: minor cleanup

This patch:
1) removes the unnecessary kref.h include file
2) removes unnecessary pointer validation from read and poll routines.
(Neither poll nor read may be called unless a call to open succeeds. A
successful call to open will always set the file private_data pointer.
Verifying that it is not null is therefore unnecessary. The associated
release and mmap calls currently ignore this check.)
3) adds a space to syslog output.
4) removes an unused function prototype.

Signed-off-by: David Ellingsworth <david@identd.dyndns.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>