net: b44: always select CONFIG_FIXED_PHY

net: b44: always select CONFIG_FIXED_PHY

When CONFIG_FIXED_PHY=m but CONFIG_B44=y, the kernel fails to link:

ld.lld: error: undefined symbol: fixed_phy_unregister
>>> referenced by b44.c
>>>               drivers/net/ethernet/broadcom/b44.o:(b44_remove_one) in archive vmlinux.a

ld.lld: error: undefined symbol: fixed_phy_register_100fd
>>> referenced by b44.c
>>>               drivers/net/ethernet/broadcom/b44.o:(b44_register_phy_one) in archive vmlinux.a

The fixed phy support is small enough that just always enabling it
for b44 is the simplest solution, and it avoids adding ugly #ifdef
checks.

Fixes: 10d2f15afba2 ("net: b44: register a fixed phy using fixed_phy_register_100fd if needed")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Link: https://patch.msgid.link/20260320154927.674555-1-arnd@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>