watchdog: hpwdt (10/12): Use "decoding" instead of "sourcing"

The term "decoding" more clearly explains what hpwdt is doing. It isn't
just finding the source of the interrupt, but rather aids in decoding what
the interrupt means.

Signed-off-by: dann frazier <dannf@hp.com>
Acked-by: Thomas Mingarelli <Thomas.Mingarelli@hp.com>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>