net: qed: Remove redundant NULL checks after list_first_entry()

net: qed: Remove redundant NULL checks after list_first_entry()

list_first_entry() never returns NULL — if the list is empty, it still
returns a pointer to an invalid object, leading to potential invalid
memory access when dereferenced.
The calls to list_first_entry() are always guarded by !list_empty(),
which guarantees a valid entry is returned. Therefore, the additional
`if (!p_buffer) break;` checks in qed_ooo_release_connection_isles(),
qed_ooo_release_all_isles(), and qed_ooo_free() are redundant and
unreachable.

Remove the dead code for clarity and consistency with common list
handling patterns in the kernel. No functional change intended.

Signed-off-by: Zhen Ni <zhen.ni@easystack.cn>
Link: https://patch.msgid.link/20250924030219.1252773-1-zhen.ni@easystack.cn
Signed-off-by: Jakub Kicinski <kuba@kernel.org>