mmc: dw_mmc-hi3798cv200: Remove unneeded assignment

The err is being set to 0 and replaced every time after this
assignment. Remove this assignment as it is extraneous.

Signed-off-by: Muhammad Usama Anjum <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Ulf Hansson <[e-mail]>

drivers/mmc/host/dw_mmc-hi3798cv200.c

···
 			goto tuning_out;
 
 		prev_err = err;
-		err = 0;
 	}
 
 tuning_out: