mmc: dw_mmc: Avoid accessing registers in runtime suspended state

mmc: dw_mmc: Avoid accessing registers in runtime suspended state

cat /sys/kernel/debug/mmc0/regs will hang up the system since
it's in runtime suspended state, so the genpd and biu_clk is
off. This patch fixes this problem by calling pm_runtime_get_sync
to wake it up before reading the registers.

Fixes: e9ed8835e990 ("mmc: dw_mmc: add runtime PM callback")
Cc: <[email protected]>
Signed-off-by: Shawn Lin <[email protected]>
Reviewed-by: Jaehoon Chung <[email protected]>
Signed-off-by: Ulf Hansson <[email protected]>