Rearrange code for initialization of 'intvl' variable
This fixes warning that the variable may be used uninitialized when
compiled with GCC 8, env CROSS_TOOLCHAIN=riscv64-gcc TARGET=riscv
TARGET_ARCH=riscv64, and WARNS=6.
Submitted by: Ján Sučan <sucanjan@gmail.com>
Sponsored by: Google, inc. (Google Summer of Code 2019)