mmc: mmc_test: Remove set-but-unused variable.

Fixes:

drivers/mmc/card/mmc_test.c: In function ‘mmc_test_seq_perf’:
drivers/mmc/card/mmc_test.c:1878:28: warning: variable ‘ts’ set but not
used [-Wunused-but-set-variable]

There's no reason to be calling timespec_sub() here, because
mmc_test_print_avg_rate() is going to do that itself.

Signed-off-by: Chris Ball <[e-mail]>
Cc: Adrian Hunter <[e-mail]>

drivers/mmc/card/mmc_test.c

···
 			     unsigned int tot_sz, int max_scatter)
 {
 	unsigned int dev_addr, i, cnt, sz, ssz;
-	struct timespec ts1, ts2, ts;
+	struct timespec ts1, ts2;
 	int ret;
 
 	sz = test->area.max_tfr;
···
 	}
 	getnstimeofday(&ts2);
 
-	ts = timespec_sub(ts2, ts1);
 	mmc_test_print_avg_rate(test, sz, cnt, &ts1, &ts2);
 
 	return 0;