[PARISC] Properly specify index field to I/D cache flush ops

replace use of "0" with "%r0" since PA 1.1 I/D flush ops only take a
general register and not an immediate value for the index field.
This just forces the code to always be PA 1.1 "clean".

From: Joel Soete <soete.joel@tiscali.be>
Signed-off-by: Grant Grundler <grundler@parisc-linux.org>

Signed-off-by: Kyle McMartin <kyle@parisc-linux.org>