efi/loongarch: Directly position the loaded image file

[ Upstream commit 174a0c56 ]

The use of the 'kernel_offset' variable to position the image file that
has been loaded by UEFI or GRUB is unnecessary, because we can directly
position the loaded image file through using the image_base field of the
efi_loaded_image struct provided by UEFI.

Replace kernel_offset with image_base to position the image file that has
been loaded by UEFI or GRUB.

Signed-off-by: Wang Yao <wangyao@lemote.com>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Stable-dep-of: beb28000 ("LoongArch: Fix entry point in kernel image header")
Signed-off-by: Sasha Levin <sashal@kernel.org>