dmaengine: PL08x: get rid of pl08x_prep_channel_resources

This function is now unnecessary; we can move its internals inline
instead.

Acked-by: Linus Walleij <linus.walleij@linaro.org>
Tested-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>