riscv: fix boolconv.cocci warnings

arch/riscv/mm/init.c:48:11-16: WARNING: conversion to bool not needed here

 Remove unneeded conversion to bool

Semantic patch information:
 Relational and logical operators evaluate to bool,
 explicit conversion is overly verbose and unneeded.

Generated by: scripts/coccinelle/misc/boolconv.cocci

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: kernel test robot <lkp@intel.com>
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>