ALSA: rme96: Check the return value of pci_enable_device() in resume callback

Fixing warning message:
  sound/pci/rme96.c: In function ‘snd_rme96_resume’:
  sound/pci/rme96.c:2418:19: warning: ignoring return value of ‘pci_enable_device’, declared with attribute warn_unused_result [-Wunused-result]

Signed-off-by: Takashi Iwai <tiwai@suse.de>