power: qpnp-fg-gen3: Fix incorrect calculations

'Commit 6364691d
("power: qpnp-fg-gen3: Fix fuel-gen3 compilation issues")'
tried fixing 32 bit compilation issues by replacing do_div() with
div64_s64. However, it broke the calculations done previously by
not storing the quotient back. Fix it.

Also, since these calculations are made on unsigned integers,
replace div64_s64() with div64_u64().

CRs-Fixed: 2235300
Change-Id: I257d8b96eeb7cec35540359b02160996ef99d1a7
Signed-off-by: Subbaraman Narayanamurthy <subbaram@codeaurora.org>