char: raw: do not leak CONFIG_MAX_RAW_DEVS to userspace

char: raw: do not leak CONFIG_MAX_RAW_DEVS to userspace

include/uapi/linux/raw.h leaks CONFIG_MAX_RAW_DEVS to userspace.

Userspace programs cannot use MAX_RAW_MINORS since CONFIG_MAX_RAW_DEVS
is not available anyway.

Remove the MAX_RAW_MINORS definition from the exported header, and use
CONFIG_MAX_RAW_DEVS in drivers/char/raw.c

While I was here, I converted printk(KERN_WARNING ...) to pr_warn(...)
and stretched the warning message.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Link: https://lore.kernel.org/r/20200617083313.183184-1-masahiroy@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>