delay: correct timeout_init_us()

The function has to use read_cntpct_el0() to update the counter, and not
read_cntfrq_el0().

Change-Id: I9c676466e784c3122e9ffc2d87e66708797086e7
Signed-off-by: Yann Gautier <yann.gautier@st.com>

include/drivers/delay_timer.h

@@ -36,7 +36,7 @@ static inline uint64_t timeout_init_us(uint32_t us)
 {
 	uint64_t cnt = timeout_cnt_us2cnt(us);
 
-	cnt += read_cntfrq_el0();
+	cnt += read_cntpct_el0();
 
 	return cnt;
 }