efi/esrt: Fix some compiler warnings

Apparently I missed some compiler warnings on 32-bit platforms, where
phys_addr_t isn't the same size as void * and I casted it to make printk
work.  Obviously I should have thought "I'm printing some random type,
instead of typecasting I should check Documentation/printk-formats.txt
and see how to do it." o/~ The More You Know ☆彡 o/~

This patch also fixes one other warning about an uninitialized variable
some compiler versions seem to see.  You can't actually hit the code
path where it would be uninitialized, because there's a prior test that
would error out, but gcc hasn't figured that out.  Anyway, it now has a
test and returns the error at both places.

Signed-off-by: Peter Jones <pjones@redhat.com>
Signed-off-by: Matt Fleming <matt.fleming@intel.com>