staging/sm7xxfb: return a proper err for smtc_alloc_fb_info failure

as smtc_alloc_fb_info can fail, but we are returning the 0,
how? because the pci_enable_device succeeded, which makes the probe
return 0, and may cause panics or some strange problems at remove
when driver unloaded by modprobe -r.

so return err properly as smtc_alloc_fb_info is doing kzallocs its
good to do -ENOMEM

Signed-off-by: Devendra Naga <devendra.aaru@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>