edac: mpc85xx fix bad page calculation

Commit b4846251 ("edac: mpc85xx add
mpc83xx support") accidentally broke how a chip select's first and last
page addresses are calculated.  The page addresses are being shifted too
far right by PAGE_SHIFT.  This results in errors such as:

  EDAC MPC85xx MC1: Err addr: 0x003075c0
  EDAC MPC85xx MC1: PFN: 0x00000307
  EDAC MPC85xx MC1: PFN out of range!
  EDAC MC1: INTERNAL ERROR: row out of range (4 >= 4)
  EDAC MC1: CE - no information available: INTERNAL ERROR

The vaule of PAGE_SHIFT is already being taken into consideration during
the calculation of the 'start' and 'end' variables, thus it is not
necessary to account for it again when setting a chip select's first and
last page address.

Signed-off-by: Peter Tyser <ptyser@xes-inc.com>
Signed-off-by: Doug Thompson <dougthompson@xmission.com>
Cc: Ira W. Snyder <iws@ovro.caltech.edu>
Cc: Kumar Gala <galak@gate.crashing.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>