slg51002: retry probe if any given gpio is missing

If optional GPIO are provisioned from the device tree, need to retry
probe if can't be acquired. This is to avoid peripherals unable to power
up.

Bug: 323257752
Test: build pass
Change-Id: I3c684d2bcc3325451cbe5a3c7017d253efbbaf1e
Signed-off-by: Kamal Shafi <kamalshafi@google.com>