efi_loader: correct block IO alignment check

If the field Media->IoAlign of the EFI block IO protocol is zero, no
alignment is required. Our code required 4 GiB alignment in this case.

Don't check buffer alignment if Media->IoAlign == 0.

Fixes: f59f0825 ("efi_loader: parameter checks BLOCK_IO_PROTOCOL")
Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>