media: i2c: dw9714: fix optional regulator support

squash with Angus patch and describe optional regulator and suspend
handling
4 jobs for dw9714_suspend in 93 minutes and 17 seconds
Status Name Job ID Coverage
  Build
passed build:aarch64 #378072
librem5

00:20:47

passed build:deb #378022
librem5:arm64

01:12:30

failed build:aarch64 #378053
librem5 allowed to fail

00:00:20

failed build:aarch64 #378021
librem5 allowed to fail

00:00:43