media: hdpvr: remove redundant assignment to retval

Variable retval is initialized to a value that is never read
so this assignment is redundant.  Clean up the code by removing
retval completely and just return the error return from the
call to i2c_add_adapter.

Addresses-Coverity: ("Unused value")

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>