staging: unisys: refactor virthba_ISR()

Fix CamelCase names:

virthba_ISR => virthba_isr
pChannelHeader => channel_header

Update all references to the modified names.

Signed-off-by: Benjamin Romer <benjamin.romer@unisys.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>