soc: qcom: mdt_loader: Actually use the e_phoff

soc: qcom: mdt_loader: Actually use the e_phoff

Rather than relying/assuming that the tools generating the firmware
places the program headers immediately following the ELF header, use
e_phoff as intended to find the program headers.

Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
Signed-off-by: Bjorn Andersson <bjorn.andersson@oss.qualcomm.com>
Link: https://lore.kernel.org/r/20250610-mdt-loader-validation-and-fixes-v2-3-f7073e9ab899@oss.qualcomm.com
Signed-off-by: Bjorn Andersson <andersson@kernel.org>