unifying variable names and usage

- In `clint_reg_write`, there are two variable names with the same
  meaning: `lowwer` and `lower`. These should be unified as `lower`.
- In `clint_update_interrupts`, although `&hart->time` and
  `&clint->mtime` are kept in sync, semantically, `&clint->mtime` should
  be used when comparing against mtimecmp.

Author: Mes0903

clint.c

@@ -6,7 +6,7 @@
 void clint_update_interrupts(hart_t *hart, clint_state_t *clint)
 {
     uint64_t time_delta =
-        clint->mtimecmp[hart->mhartid] - semu_timer_get(&hart->time);
+        clint->mtimecmp[hart->mhartid] - semu_timer_get(&clint->mtime);
     if ((int64_t) time_delta <= 0)
         hart->sip |= RV_INT_STI_BIT;
     else
@@ -50,13 +50,13 @@ static bool clint_reg_write(clint_state_t *clint, uint32_t addr, uint32_t value)
     if (addr < 0xBFF8) {
         addr -= 0x4000;
         int32_t upper = clint->mtimecmp[addr >> 3] >> 32;
-        int32_t lowwer = clint->mtimecmp[addr >> 3];
+        int32_t lower = clint->mtimecmp[addr >> 3];
         if (addr & 0b100)
             upper = value;
         else
-            lowwer = value;
+            lower = value;
 
-        clint->mtimecmp[addr >> 3] = (uint64_t) upper << 32 | lowwer;
+        clint->mtimecmp[addr >> 3] = (uint64_t) upper << 32 | lower;
         return true;
     }