regulator: fan53555: change the initcall level for fan53555 regulator

Change the initcall level of fan53555 regulator driver from
module_init() to subsys_initcall() so that the fan53555 regulator
devices can be available earlier for other clients.

CRs-Fixed: 991249
Change-Id: I4f3f4267396ec2b549235a70764d83ce86dcf38d
Signed-off-by: Subbaraman Narayanamurthy <subbaram@codeaurora.org>