media: lm3646: remove redundant assignment to variable rval

The variable rval is being initialized with a value that
is never read and is being re-assigned a little later on. The
assignment is redundant and hence can be removed.

Addresses-Coverity: ("Unused value")

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>