efi_loader: Trim output buffer size correctly for tee variables

The current code does not trim the output buffer correctly.
In fact it doesn't trim the buffer at all, since it calculates a wrong
value for it, which isn't even applied.
So let's remove the unused temporary size variable and trim the buffer
correctly.
Since we are editing efi_get_next_variable_name_int(), fix an indentation
error along the way.

Fixes: f042e47e ("efi_loader: Implement EFI variable handling via OP-TEE")
Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>

Remove superfluous conversion to (u8 *) for memcpy argument.
Reviewed-by: Heinrich Schuchardt <xypron.glpk@gmx.de>