ARM: PL08x: prevent dma_set_runtime_config() reconfiguring memcpy channels

Prevent dma_set_runtime_config() being used to alter the configuration
supplied by the platform for memcpy channel configuration.  No one
should be trying to change this configuration.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Acked-by: Linus Walleij <linus.walleij@stericsson.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>