efi: fix documentation warnings

This fixes the following warnings:

  ./lib/efi_loader/efi_firmware.c:283: warning: Function parameter or member 'package_version' not described in 'efi_firmware_fit_get_image_info'
  ./lib/efi_loader/efi_firmware.c:283: warning: Function parameter or member 'package_version_name' not described in 'efi_firmware_fit_get_image_info'
  ./lib/efi_loader/efi_firmware.c:369: warning: bad line: firmware image
  ./lib/efi_loader/efi_firmware.c:395: warning: Function parameter or member 'package_version' not described in 'efi_firmware_raw_get_image_info'
  ./lib/efi_loader/efi_firmware.c:395: warning: Function parameter or member 'package_version_name' not described in 'efi_firmware_raw_get_image_info'

Signed-off-by: Vincent Stehlé <vincent.stehle@arm.com>
Cc: Heinrich Schuchardt <xypron.glpk@gmx.de>
Reviewed-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>