efi/libstub/x86: Remove redundant assignment to pointer hdr

The pointer hdr is being assigned a value that is never read and
it is being updated later with a new value. The assignment is
redundant and can be removed.

Addresses-Coverity: ("Unused value")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20200402102537.503103-1-colin.king@canonical.com
Link: https://lore.kernel.org/r/20200409130434.6736-3-ardb@kernel.org