iio: adc: at91: make array startup_lookup static

Don't populate array startup_lookup on the stack but instead make
it static.  Makes the object code smaller.

Before:
   text	   data	    bss	    dec	    hex	filename
  21754	   5440	    128	  27322	   6aba	drivers/iio/adc/at91_adc.o

After:
   text	   data	    bss	    dec	    hex	filename
  21613	   5496	    128	  27237	   6a65	drivers/iio/adc/at91_adc.o

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/adc/at91_adc.c

@@ -799,7 +799,7 @@ static u32 calc_startup_ticks_9x5(u32 startup_time, u32 adc_clk_khz)
 	 * For sama5d3x and at91sam9x5, the formula changes to:
 	 * Startup Time = <lookup_table_value> / ADC Clock
 	 */
-	const int startup_lookup[] = {
+	static const int startup_lookup[] = {
 		0,   8,   16,  24,
 		64,  80,  96,  112,
 		512, 576, 640, 704,