bsps/arm: fix Cortex-M7 systick reload value

- see ARM DUI 0646C Arm Cortex-M7 Devices Generic User Guide
  "The RELOAD value is calculated according to its use.
  For example, to generate a multi-shot timer with a period
  of N processor clock cycles, use a RELOAD value of N-1.
  If the SysTick interrupt is required every 100 clock pulses,
  set RELOAD to 99."
- see routines used in CMSIS project for reference

Close #4746.

bsps/arm/shared/clock/clock-armv7m.c

@@ -90,7 +90,7 @@ static void _ARMV7M_Clock_initialize_early(void)
 
   interval = (uint32_t) ((freq * us_per_tick) / 1000000);
 
-  systick->rvr = interval;
+  systick->rvr = interval - 1;
   systick->cvr = 0;
   systick->csr = ARMV7M_SYSTICK_CSR_ENABLE | ARMV7M_SYSTICK_CSR_CLKSOURCE;
 }