Remove redundant variable definition

The same Volume variable is defined with two names in the same scope.
Merge the names and remove one of the definitions.

Change-Id: I021697b42791bc6323c5fa0d9704d27ecfe2c8c1
(cherry picked from commit d98fabe2aa8df0e421a69130c1d787705209682d)
Do data/media checks first in format_device()

Wait to define a Volume variable until data/media checks are done
in case the Volume definition is unnecessary.

Change-Id: I6912b1b2a473ea8737ea3e415e9a0172bb35eff1
(cherry picked from commit dd812777f0bbb7075da8c3da6a18612fa90e100e)