BACKPORT: FROMLIST: firmware_loader: fix memory leak for paged buffer

vfree() is being called on paged buffer allocated
using alloc_page() and mapped using vmap().

Freeing of pages in __vunmap() relies on nr_pages of
struct vm_struct. vmap() does not update nr_pages.

Bug: 166705104
Link: https://lore.kernel.org/patchwork/patch/1292695/


Change-Id: I8d9610d89f2936edc01b977ceba1853b41d5c249
Signed-off-by: Prateek Sood <prsood@codeaurora.org>