mtd: hyperbus: hbmc-am654: Drop pm_runtime* calls from probe

Recent genpd changes for K3 platform ensure device is ON before driver
probe is called. Therefore, drop redundant pm_runtime_* calls from
driver to simplify the code.

Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>
Link: https://lore.kernel.org/r/20200924081214.16934-4-vigneshr@ti.com