staging: Update TODO for rts5139 and rts_pstor

These are each >20k LOC drivers that embed an entire SD stack, and present
SD cards as if they were SCSI devices; both drivers should be rewritten to
be small hooks that connect the PCI (for rts_pstor) or USB (for rts5139)
hardware into Linux's MMC/xD/memorystick stacks.

Signed-off-by: Chris Ball <cjb@laptop.org>
Cc: edwin_rong <edwin_rong@realsil.com.cn>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>