dmaengine: xilinx: xdma: Fix regmap init error handling

dmaengine: xilinx: xdma: Fix regmap init error handling

devm_regmap_init_mmio returns an ERR_PTR() upon error, not NULL.
Fix the error check and also fix the error message. Use the error code
from ERR_PTR() instead of the wrong value in ret.

Fixes: 17ce252266c7 ("dmaengine: xilinx: xdma: Add xilinx xdma driver")
Signed-off-by: Alexander Stein <alexander.stein@ew.tq-group.com>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Link: https://patch.msgid.link/20251014061309.283468-1-alexander.stein@ew.tq-group.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>