mtd: pxa3xx_nand: don't duplicate MTD suspend/resume

mtd_{suspend,resume}() get called from mtdcore in a class suspend/resume
callback. We don't need to call them again here. In practice, this would
actually work OK, as nand_base actually handles nesting OK -- it just
might print warnings.

Untested, but there are few (no?) users of PM for this driver AFAIK.

Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Tested-by: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>
Acked-by: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>