mmc: dw_mmc: Remove prev_state and state assignment for STATE_SENDING_CMD

Clang reports a compile warning:
drivers/mmc/host/dw_mmc.c:2124:5: warning: Value stored to 'prev_state'
is never read

By checking the code, prev_state and state assignment for
STATE_SENDING_CMD is indeed never used after jumping to unlock tag.
So remove it.
Signed-off-by: Shawn Lin <shawn.lin@rock-chips.com>
Acked-by: Jaehoon Chung <jh80.chung@samsung.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

drivers/mmc/host/dw_mmc.c

@@ -2001,7 +2001,6 @@ static void dw_mci_tasklet_func(unsigned long priv)
 			set_bit(EVENT_CMD_COMPLETE, &host->completed_events);
 			err = dw_mci_command_complete(host, cmd);
 			if (cmd == mrq->sbc && !err) {
-				prev_state = state = STATE_SENDING_CMD;
 				__dw_mci_start_request(host, host->slot,
 						       mrq->cmd);
 				goto unlock;