pimd: Replace ALL_LIST_ELEMENTS_RO to ALL_LIST_ELEMENTS group_list iteration

pimd: Replace ALL_LIST_ELEMENTS_RO to ALL_LIST_ELEMENTS group_list iteration

To reproduce:
```
ip pim ssm prefix-list pim-ssm-group
ip prefix-list pim-ssm-group seq 10 permit 238.4.0.0/16 ge 32 le 32
```

Assert:
```
pimd[645545]: pimd/pim_igmp.c:148: igmp_source_forward_reevaluate_all(): assertion ((srcnode)->data != NULL) failed
PIM[645545]: Received signal 6 at 1649140750 (si_addr 0x6e0009d9a9, PC 0x7fe5e3f95ce1); aborting...
PIM[645545]: /usr/local/lib/libfrr.so.0(zlog_backtrace_sigsafe+0x5e) [0x7fe5e41f2d7e]
PIM[645545]: /usr/local/lib/libfrr.so.0(zlog_signal+0xe6) [0x7fe5e41f2f56]
PIM[645545]: /usr/local/lib/libfrr.so.0(+0xc9412) [0x7fe5e421d412]
PIM[645545]: /lib/x86_64-linux-gnu/libpthread.so.0(+0x14140) [0x7fe5e4133140]
PIM[645545]: /lib/x86_64-linux-gnu/libc.so.6(gsignal+0x141) [0x7fe5e3f95ce1]
PIM[645545]: /lib/x86_64-linux-gnu/libc.so.6(abort+0x123) [0x7fe5e3f7f537]
PIM[645545]: /usr/local/lib/libfrr.so.0(_zlog_assert_failed+0xd7) [0x7fe5e4246c37]
PIM[645545]: /usr/lib/frr/pimd(igmp_source_forward_reevaluate_all+0x230) [0x5638c65e3d90]
PIM[645545]: /usr/lib/frr/pimd(pim_prefix_list_update+0x53) [0x5638c65cbbf3]
PIM[645545]: /usr/local/lib/libfrr.so.0(prefix_list_entry_update_start+0x82) [0x7fe5e420a0a2]
```

Signed-off-by: Donatas Abraitis <donatas@opensourcerouting.org>