hwmon: (w83791d) Fix NULL pointer dereference by removing unnecessary structure field

hwmon: (w83791d) Fix NULL pointer dereference by removing unnecessary structure field

If driver read val value sufficient for
(val & 0x08) && (!(val & 0x80)) && ((val & 0x7) == ((val >> 4) & 0x7))
from device then Null pointer dereference occurs.
(It is possible if tmp = 0b0xyz1xyz, where same literals mean same numbers)
Also lm75[] does not serve a purpose anymore after switching to
devm_i2c_new_dummy_device() in w83791d_detect_subclients().

The patch fixes possible NULL pointer dereference by removing lm75[].

Found by Linux Driver Verification project (linuxtesting.org).

Cc: stable@vger.kernel.org
Signed-off-by: Nadezda Lutovinova <lutovinova@ispras.ru>
Link: https://lore.kernel.org/r/20210921155153.28098-1-lutovinova@ispras.ru
[groeck: Dropped unnecessary continuation lines, fixed multi-line alignment]
Signed-off-by: Guenter Roeck <linux@roeck-us.net>