qed: fix link config error handling

gcc-8 notices that qed_mcp_get_transceiver_data() may fail to
return a result to the caller:

drivers/net/ethernet/qlogic/qed/qed_mcp.c: In function 'qed_mcp_trans_speed_mask':
drivers/net/ethernet/qlogic/qed/qed_mcp.c:1955:2: error: 'transceiver_type' may be used uninitialized in this function [-Werror=maybe-uninitialized]

When an error is returned by qed_mcp_get_transceiver_data(), we
should propagate that to the caller of qed_mcp_trans_speed_mask()
rather than continuing with uninitialized data.

Fixes: c56a8be7 ("qed: Add supported link and advertise link to display in ethtool.")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: David S. Miller <davem@davemloft.net>