media: i2c: ov5670: Properly handle !CONFIG_HAVE_CLK

media: i2c: ov5670: Properly handle !CONFIG_HAVE_CLK

The ov5670 driver tries to get a reference to the xvclk provider by using
the common cock framework and deflects to parsing the "clock-frequency"
property in case the clock provider is not specified in the firmware
interface, detected by checking if ov5670->xvclk == PTR_ERR(-ENOENT).

However, as reported by the Smatch static checker, if CONFIG_HAVE_CLK is
not enabled, devm_clk_get() returns 0 which when passed to PTR_ERR()
means success causing the driver to fail without propagating any error
code up.

Explicitly handle the case where ov5670->xvclk it set to NULL, forcing
the code to parse the "clock-frequency" property in case CONFIG_HAVE_CLK
is not enabled, as suggested by Dan Carpenter.

Reported-by: Dan Carpenter <error27@gmail.com>
Suggested-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: Jacopo Mondi <jacopo.mondi@ideasonboard.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>