lowmemorykiller: use module_param_cb instead of __module_param_call

lowmemorykiller: use module_param_cb instead of __module_param_call

Use module_param_cb helper routine instead of
__module_param_call otherwise we run into following
build error:

  CC      drivers/staging/android/lowmemorykiller.o
drivers/staging/android/lowmemorykiller.c:293:28: error: macro "__module_param_call" requires 7 arguments, but only 6 given
       S_IRUGO | S_IWUSR, -1);
                            ^
drivers/staging/android/lowmemorykiller.c:290:1: warning: data definition has no type or storage class [enabled by default]
 __module_param_call(MODULE_PARAM_PREFIX, adj,
 ^
drivers/staging/android/lowmemorykiller.c:290:1: error: type defaults to ‘int’ in declaration of ‘__module_param_call’ [-Werror=implicit-int]
drivers/staging/android/lowmemorykiller.c:273:32: warning: ‘lowmem_adj_array_ops’ defined but not used [-Wunused-variable]
 static struct kernel_param_ops lowmem_adj_array_ops = {
                                ^
cc1: some warnings being treated as errors
make[3]: *** [drivers/staging/android/lowmemorykiller.o] Error 1

Signed-off-by: Amit Pundir <amit.pundir@linaro.org>