part_efi: Drop NULL check in part_get_info_efi()

This cannot be NULL since part_get_info() calls this function and requires
it to be non-NULL.

Reported-by: Coverity (CID: 138497)

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Tom Rini <trini@konsulko.com>