avr32: fix build failures from mis-naming of atmel_nand.h

Commit bf4289cba02b ("ATMEL: fix nand ecc support") indicated that it
wanted to "Move platform data to a common header
include/linux/platform_data/atmel_nand.h" and the new header even had
re-include protectors with:

    #ifndef __ATMEL_NAND_H__

However, the file that was added was simply called atmel.h
and this caused avr32 defconfig to fail with:

  In file included from arch/avr32/boards/atstk1000/setup.c:22:
  arch/avr32/mach-at32ap/include/mach/board.h:10:44: error: linux/platform_data/atmel_nand.h: No such file or directory
  In file included from arch/avr32/boards/atstk1000/setup.c:22:
  arch/avr32/mach-at32ap/include/mach/board.h:121: warning: 'struct atmel_nand_data' declared inside parameter list
  arch/avr32/mach-at32ap/include/mach/board.h:121: warning: its scope is only this definition or declaration, which is probably not what you want
  make[2]: *** [arch/avr32/boards/atstk1000/setup.o] Error 1

It seems the scope of the file contents will expand beyond
just nand, so ignore the original intention, and fix up the
users who reference the bad name with the _nand suffix.

CC: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
CC: David Woodhouse <dwmw2@infradead.org>
Acked-by: Hans-Christian Egtvedt <egtvedt@samfundet.no>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>