android_memset.c: Use __attribute__((no_sanitize("integer")))

Turn off integer sanitization on android_memset. memset()ing is
expected to be a fast operation.

Avoid the use of the "while (size--) { }" construct, which harmlessly
underflows.

Change-Id: Ia61ff2323c759bf52df7e70b8be2fae0b0366dda