net: ax88796c: Remove pointless check in ax88796c_open()

Clang warns:

drivers/net/ethernet/asix/ax88796c_main.c:851:24: error: address of
array 'ax_local->phydev->advertising' will always evaluate to 'true'
[-Werror,-Wpointer-bool-conversion]
        if (ax_local->phydev->advertising &&
            ~~~~~~~~~~~~~~~~~~^~~~~~~~~~~ ~~

advertising cannot be NULL here if ax_local is not NULL, which cannot
happen due to the check in ax88796c_probe(). Remove the check.

Link: https://github.com/ClangBuiltLinux/linux/issues/1492


Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>