int_sqrt: Improve 3x faster integer sqrt.

Result on 10,000,000 call.
Old:
sqrt(12345689) = 3513
real	0m0.768s
user	0m0.760s
sys	0m0.004s

New:
sqrt(12345689) = 3513
real	0m0.222s
user	0m0.224s
sys	0m0.000s

Change-Id: Ib4f76de467c1610cbac79d9122fe40e4f7c63839
Signed-off-by: engstk <eng.stk@sapo.pt>
Signed-off-by: Simao Gomes Viana <xdevs23@outlook.com>