clk: at91: sckc: register slow_rc with accuracy option

Chapter 57.7.5 of SAM9X60 datasheet specifies that the maximum drift of
this oscillator is +- 3KHz. Use that value and the formula at [1]
or the calculator at [2] to compute the PPB value.

[1] https://www.everythingrf.com/rf-calculators/ppm-to-hz-calculator
[2] https://www.changpuak.ch/electronics/ppm_to_Hz_converter.php

Fixes: 04bcc42 ("clk: at91: sckc: add support for SAM9X60")
Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Link: https://lore.kernel.org/r/1595403506-8209-9-git-send-email-claudiu.beznea@microchip.com
Signed-off-by: Stephen Boyd <sboyd@kernel.org>

Author: claudiubeznea

drivers/clk/at91/sckc.c

@@ -471,8 +471,9 @@ static void __init of_sam9x60_sckc_setup(struct device_node *np)
 	if (!regbase)
 		return;
 
-	slow_rc = clk_hw_register_fixed_rate(NULL, parent_names[0], NULL, 0,
-					     32768);
+	slow_rc = clk_hw_register_fixed_rate_with_accuracy(NULL, parent_names[0],
+							   NULL, 0, 32768,
+							   93750000);
 	if (IS_ERR(slow_rc))
 		return;