misc: rtsx: make several functions static

Several helper functions are local to the source and do not
need to be in global scope, so make them static.

Cleans up sparse warnings:
symbol 'rtsx_pm_power_saving' was not declared. Should it be static?
symbol 'rtsx_set_l1off_sub_cfg_d0' was not declared. Should it be static?
symbol 'rtsx_pm_full_on' was not declared. Should it be static?
symbol 'rtsx_comm_set_ltr_latency' was not declared. Should it be static?
symbol 'rtsx_pci_process_ocp' was not declared. Should it be static?
symbol 'rtsx_pci_process_ocp_interrupt' was not declared. Should it be
static?

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>