regulator: ad5398: Fix incorrect power down bit mask

regulator: ad5398: Fix incorrect power down bit mask

AD5398_SW_POWER_DOWN was defined with a bit position outside the valid
range of the device's 16-bit register. The bitwise operation with an
unsigned short would always evaluate to 0, making the power down check
ineffective.

Update AD5398_SW_POWER_DOWN to use a valid bit position within the
16-bit range of the register.

Fixes: 19d022d67d73 ("regulator: ad5398: change enable bit name to improve readibility")
Signed-off-by: Dheeraj Reddy Jonnalagadda <dheeraj.linuxdev@gmail.com>
Link: https://patch.msgid.link/20250206103153.59114-1-dheeraj.linuxdev@gmail.com
Signed-off-by: Mark Brown <broonie@kernel.org>