lib: move phdr increment to for loop heading

lib: move phdr increment to for loop heading

Shifting this pointer in the loop will be more logical when working
with the code later, because you can see at a glance what exactly
changes at each iteration. Moreover, the code remains equivalent
because this variable is not used after the loop.

Signed-off-by: Maxim Moskalets <maximmosk4@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>