delay: Use u8, decrementing loop

Use u8 instead of i16 as a delay can never be negative and should never
block for a long period of time.

Use a decrementing loop as SDCC generates more efficient code.

Signed-off-by: Tim Crawford <tcrawford@system76.com>

src/arch/8051/include/arch/delay.h

@@ -17,6 +17,6 @@ void delay_ticks(uint16_t ticks);
 #define delay_ns(X) \
     delay_ticks((uint16_t)((((uint32_t)(X)) * 69UL + 89999UL) / 90000UL));
 
-void delay_ms(int ms);
+void delay_ms(uint8_t ms);
 
 #endif // _ARCH_DELAY_H