storaged: fix task io stats parsing

comm field in task io stats string can have comma since this field
includes task arguments. As a result, splitting the string by comma
doesn't always give 13 fields. Parse the string in following way to
fix that.

last 11 fields -> pid and io stats
Second field to 12th from last -> comm

Bug: 63739275
Change-Id: I6a2418260444c71d6492fc6cbd639d3cc54ceaed