remoteproc/ste_modem: staticize local symbols

These local symbols are used only in this file.
Fix the following sparse warnings:

drivers/remoteproc/ste_modem_rproc.c:167:27: warning: symbol 'sproc_fw_ops' was not declared. Should it be static?
drivers/remoteproc/ste_modem_rproc.c:196:25: warning: symbol 'sproc_dev_cb' was not declared. Should it be static?

Signed-off-by: Jingoo Han <jg1.han@samsung.com>
[standartize patch title]
Signed-off-by: Ohad Ben-Cohen <ohad@wizery.com>