Revert "media: atomisp: keep the ISP powered on when setting it"

changeset d0213061a501 ("media: atomisp: fix mask and shift operation on ISPSSPM0")
solved the existing issue with the IUNIT power on code.

So, the driver can now use the right code again.

This reverts commit 95d1f398.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>