fix(plat/mediatek/mt8183): fix out-of-bound access

Fix coverity checks which is found on:
https://review.trustedfirmware.org/c/TF-A/trusted-firmware-a/+/1806/comment/eaec126f_af5eb624/

Change-Id: I9405f7f67aa4115c1a7b8b4623b6b0830e62f814
Signed-off-by: Tinghan Shen <tinghan.shen@mediatek.com>

plat/mediatek/mt8183/drivers/sspm/sspm.c

@@ -149,7 +149,7 @@ int sspm_alive_show(void)
 
 	while (sspm_ipi_recv_non_blocking(IPI_ID_PLATFORM,
 					  &ipi_data,
-					  sizeof(ipi_data))
+					  sizeof(ipi_data) / sizeof(uint32_t))
 					  && count) {
 		mdelay(100);
 		count--;