Reading the contents of a module_param_string through sysfs currently
oopses because the param_get_charp() function cannot operate on a
kparam_string struct.  This introduces the required param_get_string.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>