m68knommu: use "r", not "i" constraint in cacheflush asm's

Let the compiler choose which register to use in the cache flushing
asm statements, instead of imposing %d0.

Additionally, fix two typo's.

Signed-off-by: Philippe De Muyter <phdm@macqel.be>
Signed-off-by: Greg Ungerer <gerg@uclinux.org>