Fix trivial bug in kprof -- pc not getting set correctly

I was testing with dd bs=64 etc. etc.
Andrew Gallatin tested with cat.

For me, the pc was always right, since each read was a single
record and the pc was recomputed each time. For larger reads, it would be mostly wrong.

Signed-off-by: Ronald G. Minnich <rminnich@google.com>