target/riscv/pmp.c: pmpcfg_csr_read returns bogus value on RV64

pmp_read_cfg() returns 8-bit value, which is combined together to form a single pmpcfg CSR.
The default promotion rules will result in an integer here ("i*8" is integer, which
flows through) resulting in a 32-bit signed value on most hosts.
That's bogus on RV64I, with the high bits of the CSR being wrong.

Signed-off-by: Dayeol Lee <dayeol@berkeley.edu>
Reviewed-by: Palmer Dabbelt <palmer@sifive.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Signed-off-by: Palmer Dabbelt <palmer@sifive.com>

target/riscv/pmp.c

@@ -325,7 +325,7 @@ target_ulong pmpcfg_csr_read(CPURISCVState *env, uint32_t reg_index)
 {
     int i;
     target_ulong cfg_val = 0;
-    uint8_t val = 0;
+    target_ulong val = 0;
 
     for (i = 0; i < sizeof(target_ulong); i++) {
         val = pmp_read_cfg(env, (reg_index * sizeof(target_ulong)) + i);