Kernel: Make UART::print_num(0) work on aarch64

Author: https://github.com/nico
Commit: 94d0562569
Pull-request: https://github.com/SerenityOS/serenity/pull/10276

Kernel/Prekernel/Arch/aarch64/UART.h

@@ -30,10 +30,10 @@ public:
     {
         char buf[11];
         int i = 0;
-        while (n) {
+        do {
             buf[i++] = (n % 10) + '0';
             n /= 10;
-        }
+        } while (n);
         for (i--; i >= 0; i--)
             send(buf[i]);
     }