staging: vchiq_2835_arm: Make cache-line-size a required DT property

The original github source allowed for the cache-line-size property
to be missing.  Since recent firmwares also require this property,
it makes sense to always require it in the driver as well.

If the cache-line-size property is missing, then the driver probe
should fail as no dev since the kernel and dt may be out of sync.
The fix is to add a check for the return value of of_property_read_u32.

Changes V2:
	1. Add error message if cache-line-size is missing.
	2. Simple check for non-zero return value from
	   of_property_read_u32.

Signed-off-by: Michael Zoran <mzoran@crowfest.net>
Acked-by: Stefan Wahren <stefan.wahren@i2se.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>