Documentation: dwc_pcie_pmu: Update bdf to sbdf

Update document to reflect the driver change to use sbdf instead
of bdf alone.

Signed-off-by: Krishna chaitanya chundru <quic_krichai@quicinc.com>
Reviewed-by: Yicong Yang <yangyicong@hisilicon.com>
Link: https://lore.kernel.org/r/20240816-dwc_pmu_fix-v2-2-198b8ab1077c@quicinc.com


Signed-off-by: Will Deacon <will@kernel.org>