tests/kernel/early_sleep: Fix for fast ticks

"50" ticks is fine with 100 Hz timer precision but way too short to
survive the conversion to milliseconds on fast, non-decimal tick
rates.  Make it half a second, which was the original intent.

Signed-off-by: Andy Ross <andrew.j.ross@intel.com>

tests/kernel/early_sleep/src/main.c

@@ -33,7 +33,7 @@
 
 #define THREAD_STACK		(384 + CONFIG_TEST_EXTRA_STACKSIZE)
 
-#define TEST_TICKS_TO_SLEEP	50
+#define TEST_TICKS_TO_SLEEP	(CONFIG_SYS_CLOCK_TICKS_PER_SEC / 2)
 
 /* Helper thread data */
 static K_THREAD_STACK_DEFINE(helper_tstack, THREAD_STACK);