dmaengine: tegra210-adma: fix of_irq_get() error check

of_irq_get() may return 0 as well as negative error number on failure,
while the driver only checks for the negative values. The driver would then
call request_irq(0, ...) in tegra_adma_alloc_chan_resources() and never get
valid channel interrupt.

Check for 'tdc->irq <= 0' instead and return -ENXIO from the driver's probe
iff of_irq_get() returned 0.

Fixes: f46b1957 ("dmaengine: tegra-adma: Add support for Tegra210 ADMA")
Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Acked-by: Thierry Reding <treding@nvidia.com>
Acked-by: Jon Hunter <jonathanh@nvidia.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>