memstick/ms_block: Fix a memory leak

In the Linux kernel, the following vulnerability has been resolved:

memstick/ms_block: Fix a memory leak

'erased_blocks_bitmap' is never freed. As it is allocated at the same time

as 'used_blocks_bitmap', it is likely that it should be freed also at the

same time.

Add the corresponding bitmap_free() in msb_data_clear().