usb: musb: cppi: fix build errors due to DBG and missing musb variable

Replace DBG with dev_dbg and fix invalid access of musb->controller.
With this patch cppi_dma builds successfully.

Cc: <stable@kernel.org>
Signed-off-by: Per Forlin <per.forlin@linaro.org>
Signed-off-by: Felipe Balbi <balbi@ti.com>