fix: remove unused variable warning in RISC-V codegen

Remove unused 'func_t *func' declaration in code_generate() function
that was causing compiler warnings. The variable is not needed as 'func'
is only used in emit_ph2_ir() where it has its own local declaration.

Author: jserv

src/riscv-codegen.c

@@ -446,7 +446,6 @@ void code_generate(void)
     elf_data_start = elf_code_start + elf_offset;
     elf_rodata_start = elf_data_start + elf_data->size;
     elf_bss_start = elf_rodata_start + elf_rodata->size;
-    func_t *func;
 
     /* start: save original sp in s0; allocate global stack; run init */
     emit(__addi(__s0, __sp, 0));