MIPS CS_GRP_CALL and CS_GRP_RET broken for simple case

[tnballo]

Script:

import capstone
from capstone import *

cs = Cs(CS_ARCH_MIPS, CS_MODE_32)
cs.detail = True

print(f"Capstone version: {capstone.__version__}")

call_encoding = b'\x40\x00\x00\x0c' # jal 0x100
ret_encoding = b'\x08\x00\xe0\x03'  # jr $ra

for i in cs.disasm(call_encoding, 0):
    print(f"\n0x{i.address:x}\t{i.mnemonic}\t{i.op_str}\t(Groups: {i.groups})")
    print(f"Is call? {capstone.CS_GRP_CALL in i.groups}")

for i in cs.disasm(ret_encoding, 0):
    print(f"\n0x{i.address:x}\t{i.mnemonic}\t{i.op_str}\t(Groups: {i.groups})")
    print(f"Is ret? {capstone.CS_GRP_RET in i.groups}")

Output:

Capstone version: 4.0.2

0x0	jal	0x100	(Groups: [137])
Is call? False

0x0	jr	$ra	(Groups: [137, 1])
Is ret? False

Looks like the latter was identified in #370 (old). This would really be a nice thing to fix for a wide range of binary analyses!