rtc: pm8xxx: fix unintended sign extension

BugLink: https://bugs.launchpad.net/bugs/1864773

[ Upstream commit e4228088 ]

Shifting a u8 by 24 will cause the value to be promoted to an integer. If
the top bit of the u8 is set then the following conversion to an unsigned
long will sign extend the value causing the upper 32 bits to be set in
the result.

Fix this by casting the u8 value to an unsigned long before the shift.

Detected by CoverityScan, CID#1309693 ("Unintended sign extension")

Fixes: 9a9a54ad ("drivers/rtc: add support for Qualcomm PMIC8xxx RTC")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

drivers/rtc/rtc-pm8xxx.c

@@ -186,7 +186,8 @@ static int pm8xxx_rtc_read_time(struct device *dev, struct rtc_time *tm)
 		}
 	}
 
-	secs = value[0] | (value[1] << 8) | (value[2] << 16) | (value[3] << 24);
+	secs = value[0] | (value[1] << 8) | (value[2] << 16) |
+	       ((unsigned long)value[3] << 24);
 
 	rtc_time_to_tm(secs, tm);
 
@@ -267,7 +268,8 @@ static int pm8xxx_rtc_read_alarm(struct device *dev, struct rtc_wkalrm *alarm)
 		return rc;
 	}
 
-	secs = value[0] | (value[1] << 8) | (value[2] << 16) | (value[3] << 24);
+	secs = value[0] | (value[1] << 8) | (value[2] << 16) |
+	       ((unsigned long)value[3] << 24);
 
 	rtc_time_to_tm(secs, &alarm->time);