ARM: OMAP: fix error return code in omap1_system_dma_init()

Fix to return -ENOMEM in the d->chan alloc error handling
case instead of 0, as done elsewhere in this function.

Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Signed-off-by: Tony Lindgren <tony@atomide.com>