efi_loader: Remove incorrect calls of EFI_CALL in TCG2

There is two unneeded EFI_CALL references in tcg2_measure_pe_image().
The first one in efi_search_protocol() and the second on in the device path
calculation.  The second isn't even a function we should be calling, but a
pointer assignment, which happens to work with the existing macro.

While at it switch the malloc call to a calloc, remove the unnecessary cast
and get rid of an unneeded if statement before copying the device path

Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Reviewed-by: Heinrich Schuchardt <xypron.glpk@gmx.de>