i965: Fix intel_miptree_map() signature to be more 64-bit safe

i965: Fix intel_miptree_map() signature to be more 64-bit safe

This patch should diminish the likelihood of pointer arithmetic overflow
bugs, like the one fixed by b69c7c5dac.

Change the type of parameter 'out_stride' from int to ptrdiff_t. The
logic is that if you call intel_miptree_map() and use the value of
'out_stride', then you must be doing pointer arithmetic on 'out_ptr'.
Using ptrdiff_t instead of int should make a little bit harder to hit
overflow bugs.

As a side-effect, some function-scope variables needed to be retyped to
avoid compilation errors.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Signed-off-by: Chad Versace <chad.versace@linux.intel.com>