media: ov2740: fix dereference before null check on pointer nvm

Currently pointer nvm is being dereferenced before it is being null
checked.  Fix this by moving the assignments of pointers client and
ov2740 so that are after the null check hence avoiding any potential
null pointer dereferences on pointer nvm.

Fixes: 5e6fd339 ("media: ov2740: allow OTP data access during streaming")
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+huawei@kernel.org>