recovery: fix building with pointer-to-int errors turned on

Use intptr_t/uintptr_t to cast between pointer and int to allow
building with -Werror=pointer-to-int-cast and
Werror=int-to-pointer-cast turned on.

Cast to char* instead of unsigned int for pointer arithmetic.

Change-Id: Ia862306fdcca53866b330e8cf726f3d62f2248a0