Staging: bcm2835-audio: remove unneeded NULL check

We just dereferenced "instance" on the line before so checking it here
is pointless.  Anyway, it can't be NULL here so let's remove the check.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>