staging: zcache: Fix incorrect module_param_array types

drivers/staging/zcache/zcache-main.c: In function ‘__check_disable_cleancache’:
drivers/staging/zcache/zcache-main.c:1928: warning: return from incompatible pointer type
drivers/staging/zcache/zcache-main.c: In function ‘__check_disable_frontswap’:
drivers/staging/zcache/zcache-main.c:1929: warning: return from incompatible pointer type
drivers/staging/zcache/zcache-main.c: In function ‘__check_disable_frontswap_ignore_nonactive’:
drivers/staging/zcache/zcache-main.c:1933: warning: return from incompatible pointer type

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>