media: i2c: ov4689: code cleanup

Fix minor nits from the last review round: extra {}, temporary
variables for ARRAYS_SIZE(), redundant check in ov4689_check_hwcfg.
No functional change intended.

Signed-off-by: Mikhail Rudenko <mike.rudenko@gmail.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>