RISC-V: Use IS_ENABLED(CONFIG_CMODEL_MEDLOW)

IS_ENABLED should generally use CONFIG_ prefaced symbols and
it doesn't appear as if there is a CMODEL_MEDLOW define.
Signed-off-by: Joe Perches <joe@perches.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Palmer Dabbelt <palmer@sifive.com>

arch/riscv/kernel/module.c

@@ -141,7 +141,7 @@ static int apply_r_riscv_hi20_rela(struct module *me, u32 *location,
 {
 	s32 hi20;
 
-	if (IS_ENABLED(CMODEL_MEDLOW)) {
+	if (IS_ENABLED(CONFIG_CMODEL_MEDLOW)) {
 		pr_err(
 		  "%s: target %016llx can not be addressed by the 32-bit offset from PC = %p\n",
 		  me->name, (long long)v, location);