iio: adc: at91_adc: allow to use full range of startup time

commit 2ab5f39b upstream.

The DT-Property "atmel,adc-startup-time" is stored in an u8 for a microsecond
value. When trying to increase the value of STARTUP in Register AT91_ADC_MR
some higher values can't be reached.

Change the type in function parameter and private structure field from u8 to
u32.
Signed-off-by: Jan Leupold <leupold@rsi-elektrotechnik.de>
[nicolas.ferre@atmel.com: change commit message, increase u16 to u32 for startup time]
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Acked-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>
Signed-off-by: Jiri Slaby <jslaby@suse.cz> [-js: only change at91_adc_state for 3.12]

drivers/iio/adc/at91_adc.c

@@ -55,7 +55,7 @@ struct at91_adc_state {
 	u8			num_channels;
 	void __iomem		*reg_base;
 	struct at91_adc_reg_desc *registers;
-	u8			startup_time;
+	u32			startup_time;
 	u8			sample_hold_time;
 	bool			sleep_mode;
 	struct iio_trigger	**trig;