linux-user: Fix loaddr computation for some elf files

The file offset of the load segment is not relevant to the
low address, only the beginning of the virtual address page.

Cc: qemu-stable@nongnu.org
Fixes: a93934fe ("elf: take phdr offset into account when calculating the program load address")
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1952


Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Michael Tokarev <mjt@tls.msk.ru>