ipg: naming convention fixes

This changes some camel-case names to follow proper kernel naming convention.

Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>
Cc: Francois Romieu <romieu@fr.zoreil.com>
Cc: Sorbica Shieh <sorbica@icplus.com.tw>
Cc: Jesse Huang <jesse@icplus.com.tw>
Signed-off-by: David S. Miller <davem@davemloft.net>