fm10k: mark PM functions as __maybe_unused

A cleanup of the PM code left an incorrect #ifdef in place, leading
to a harmless build warning:

drivers/net/ethernet/intel/fm10k/fm10k_pci.c:2502:12: error: 'fm10k_suspend' defined but not used [-Werror=unused-function]
drivers/net/ethernet/intel/fm10k/fm10k_pci.c:2475:12: error: 'fm10k_resume' defined but not used [-Werror=unused-function]

It's easier to use __maybe_unused attributes here, since you
can't pick the wrong one.

Fixes: 8249c47c ("fm10k: use generic PM hooks instead of legacy PCIe power hooks")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Jacob Keller <jacob.e.keller@intel.com>
Tested-by: Krishneil Singh <krishneil.k.singh@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>