staging: greybus/timesync: avoid divide by zero on X86 Qemu

A system configured without CONFIG_CPUFREQ will return 0 for cpufreq_get().
greybus-timesync can subsequently then do a divide-by-zero as result. This
patch fixes by checking for a zero return value from cpufreq_get() and
setting to a default value of 19.2MHz.

Reported-by: Rui Miguel Silva <[e-mail]>
Signed-off-by: Bryan O'Donoghue <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/staging/greybus/timesync_platform.c

···
 #include "greybus.h"
 #include "arche_platform.h"
 
+#define DEFAULT_FRAMETIME_CLOCK_HZ 19200000
+
 static u32 gb_timesync_clock_frequency;
 int (*arche_platform_change_state_cb)(enum arche_platform_state state,
 				      struct gb_timesync_svc *pdata);
···
 
 u32 gb_timesync_platform_get_clock_rate(void)
 {
-	if (unlikely(!gb_timesync_clock_frequency))
-		return cpufreq_get(0);
+	if (unlikely(!gb_timesync_clock_frequency)) {
+		gb_timesync_clock_frequency = cpufreq_get(0);
+		if (!gb_timesync_clock_frequency)
+			gb_timesync_clock_frequency = DEFAULT_FRAMETIME_CLOCK_HZ;
+	}
 
 	return gb_timesync_clock_frequency;
 }