printk: fix build warning when CONFIG_PRINTK=n

build warning when CONFIG_PRINTK=n
	kernel/printk/printk.c:175:5: warning: no previous prototype for
	 'devkmsg_sysctl_set_loglvl' [-Wmissing-prototypes]

devkmsg_sysctl_set_loglvl() is only used in sysctl.c when CONFIG_PRINTK=y,
but it participates in the build when CONFIG_PRINTK=n. So add compile
dependency CONFIG_PRINTK=y && CONFIG_SYSCTL=y to fix the build warning.

Signed-off-by: Xiaoming Ni <nixiaoming@huawei.com>
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
3 files changed