media: ov5647: Fix return value from read/write

The ov5647_read()/ov5647_write() return in case of success the number
of bytes read or written respectively. This requires callers to check
if the return value is less than zero to detect an error. Unfortunately,
in several places, callers directly return the result of a read/write
call, causing issues when the returned valued is checked to be different
from zero to detect an error.

Fix this by returning zero if i2c_master_send() and i2c_master_read()
return a positive value (the number of bytes written or read).

Signed-off-by: Jacopo Mondi <jacopo@jmondi.org>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>