drivers/misc/ad525x_dpot: AD5274 fix RDAC read back errors

[ Upstream commit f3df53e4d70b5736368a8fe8aa1bb70c1cb1f577 ]

Fix RDAC read back errors caused by a typo. Value must shift by 2.

Fixes: a4bd3949 ("drivers/misc/ad525x_dpot.c: new features")
Signed-off-by: Michael Hennerich <michael.hennerich@analog.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>