Staging: fbtft: Fix bug in fbtft-core

Commit 367e8560 introduced a bug
in fbtft-core where fps is always 0, this is because variable
update_time is not assigned correctly.
Signed-off-by: Ksenija Stanojevic <ksenija.stanojevic@gmail.com>
Fixes: 367e8560 ("Staging: fbtbt: Replace timespec with ktime_t")
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/fbtft/fbtft-core.c

@@ -391,11 +391,11 @@ static void fbtft_update_display(struct fbtft_par *par, unsigned int start_line,
 
 	if (unlikely(timeit)) {
 		ts_end = ktime_get();
-		if (ktime_to_ns(par->update_time))
+		if (!ktime_to_ns(par->update_time))
 			par->update_time = ts_start;
 
-		par->update_time = ts_start;
 		fps = ktime_us_delta(ts_start, par->update_time);
+		par->update_time = ts_start;
 		fps = fps ? 1000000 / fps : 0;
 
 		throughput = ktime_us_delta(ts_end, ts_start);