iio:adc:at91-sama5d2: make array startup_lookup static to reduce code size

Making the const array startup_lookup static rather having it on the
stack saves 69 bytes. Add in missing int specifier to clean up a
checkpatch warning.

Before:
   text	   data	    bss	    dec	    hex	filename
  10297	   2800	    128	  13225	   33a9	drivers/iio/adc/at91-sama5d2_adc.o

After:
   text	   data	    bss	    dec	    hex	filename
  10140	   2888	    128	  13156	   3364	drivers/iio/adc/at91-sama5d2_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-sama5d2_adc.c

@@ -411,7 +411,7 @@ static int at91_adc_buffer_init(struct iio_dev *indio)
 static unsigned at91_adc_startup_time(unsigned startup_time_min,
 				      unsigned adc_clk_khz)
 {
-	const unsigned startup_lookup[] = {
+	static const unsigned int startup_lookup[] = {
 		  0,   8,  16,  24,
 		 64,  80,  96, 112,
 		512, 576, 640, 704,