raw: set range for MAX_RAW_DEVS

The Kconfig symbol MAX_RAW_DEVS is meant to be between 1 and 65536. But
those boundaries are not enforced by its Kconfig entry.

Note that MAX_RAW_DEVS is used to set MAX_RAW_MINORS in
drivers/char/raw.c. If one would accidentally set MAX_RAW_DEVS to an
invalid value, that invalid value will actually end up being used in
raw_init().

So add an appropriate range to this Kconfig entry.

Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>