mtd: mtd_torturetest can cause stack overflows

mtd_torturetest uses the module parm "ebcnt" to control the size of a
stack based array of int's. When "ebcnt" is large, Ex: 1000, it
causes stack overflows on systems with small kernel stacks. The fix
is to move the array from the stack to kmalloc memory.

Signed-off-by: Al Cooper <alcooperx@gmail.com>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>