[MTD] m25p80: chip erase != block erase != sector erase

This fixes broken terminology added in the "m25p80.c erase enhance" patch,
which added a chip erase command but called it "block erase".  There are
already two block erase commands; blocks are 4KiB or 32KiB.  There's also
a sector erase (usually 64 KiB).  Chip erase typically covers Megabytes.

  OPCODE_BE   ==> OPCODE_CHIP_ERASE
  erase_block ==> erase_chip

[dbrownell@users.sourceforge.net: update sector erase comments too ]

Signed-off-by: Chen Gong <clumsycg@gmail.com>
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>