hostap: hide unused procfs helpers

When CONFIG_PROC_FS isn't set, gcc warning this:

drivers/net/wireless/intersil/hostap/hostap_hw.c:2901:12: warning: ‘prism2_registers_proc_show’ defined but not used [-Wunused-function]
 static int prism2_registers_proc_show(struct seq_file *m, void *v)

drivers/net/wireless/intersil/hostap/hostap_proc.c:16:12: warning: ‘prism2_debug_proc_show’ defined but not used [-Wunused-function]
 static int prism2_debug_proc_show(struct seq_file *m, void *v)
            ^
drivers/net/wireless/intersil/hostap/hostap_proc.c:49:12: warning: ‘prism2_stats_proc_show’ defined but not used [-Wunused-function]
 static int prism2_stats_proc_show(struct seq_file *m, void *v)
            ^
drivers/net/wireless/intersil/hostap/hostap_proc.c:177:12: warning: ‘prism2_crypt_proc_show’ defined but not used [-Wunused-function]
 static int prism2_crypt_proc_show(struct seq_file *m, void *v)
            ^

fix this by adding #ifdef around them.
hfa384x_read_reg is only used by prism2_registers_proc_show,so move it
into #ifdef.

Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>