dma: tegra: make data used as *of_device_id.data const

Since of_device_id.data is declared as a pointer to const data a few
more consts can be added in this driver.

[ukl: split Laxman's patch to prevent warnings in the middle of the
series. Original patch was sent with msgid
1346217447-19730-1-git-send-email-ldewangan@nvidia.com]

Signed-off-by: Laxman Dewangan <ldewangan@nvidia.com>
Acked-by: Stephen Warren <swarren@wwwdotorg.org>
Acked-by: Vinod Koul <vinod.koul@linux.intel.com>
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>