[netdrvr sis190] remove unneeded alignment code, other small fixes

[netdrvr sis190] remove unneeded alignment code, other small fixes

Driver does not need to enforce 256 byte alignment for data returned
from pci_alloc_consistent().
- {rx/tx}_dma_aligned and {rx/td}_dma_raw are both replaced by {rx/tx}_dma;
- {rx/tx}_desc_raw is replaced by direct use of {Rx/Tx}DescArray;
- SiS190_open()
  + fixup for a lack of kmalloc() failure handling;
  + (return status) there is no need for both retval/rc: merge them;
  + anonymous printk() fixup: the name of the guilty device is printed;
- define {RX/TX}_DESC_TOTAL_SIZE because I am too lazy to read twice the
  same lengthy arithmetic expression.