hwmon: (pmbus/mp2975) Add error check for pmbus_read_word_data() return value

hwmon: (pmbus/mp2975) Add error check for pmbus_read_word_data() return value

mp2973_read_word_data() XORs the return value of pmbus_read_word_data()
with PB_STATUS_POWER_GOOD_N without first checking for errors. If the I2C
transaction fails, a negative error code is XORed with the constant,
producing a corrupted value that is returned as valid status data instead
of propagating the error.

Add the missing error check before modifying the return value.

Fixes: acda945afb465 ("hwmon: (pmbus/mp2975) Fix PGOOD in READ_STATUS_WORD")
Cc: stable@vger.kernel.org
Signed-off-by: Sanman Pradhan <psanman@juniper.net>
Link: https://lore.kernel.org/r/20260317173308.382545-3-sanman.pradhan@hpe.com
Signed-off-by: Guenter Roeck <linux@roeck-us.net>