mtd: brcmnand: do not make local variable static

Remove static in front of ctrl. This variable should not be shared
between different instances of brcmnand_probe(), it should be local to
this function and stored on the stack.

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>