nconfig: Fix segfault when help contains special characters

nconfig segfaults when help text contains the character '%'. For a quick
example, navigate to the kernel compression options and get the help for
bzip2. Doing so triggers a call to mvwprintw() with a string containing
'%' and no extra arguments to fill in the specifier's value. Fix this
case by printing the literal string retrieved from the kconfig.

 #0  0x00002b52b6b11d83 in vfprintf () from /lib/libc.so.6
 #1  0x00002b52b6bad010 in __vsnprintf_chk () from /lib/libc.so.6
 #2  0x00002b52b623991b in _nc_printf_string () from
 /lib/libncursesw.so.5
 #3  0x00002b52b6234cff in vwprintw () from /lib/libncursesw.so.5
 #4  0x00002b52b6234db9 in mvwprintw () from /lib/libncursesw.so.5
 #5  0x00000000004151d8 in fill_window (win=0x21b64c0,
     text=0x21b62b0 "CONFIG_KERNEL_BZIP2:\n\nIts compression ratio and
     speed is intermediate.\nDecompression speed is slowest among the
     three.  The kernel\nsize is about 10% smaller with bzip2, in
     comparison to gzip.\nBzip2 us"...)
     at scripts/kconfig/nconf.gui.c:229
 #6  0x0000000000416335 in show_scroll_win (main_window=0x21a5630,
         title=0x157fa30 "Bzip2",
 	    text=0x21b62b0 "CONFIG_KERNEL_BZIP2:\n\nIts compression
 	    ratio and speed is intermediate.\nDecompression speed is
 	    slowest among the three.  The kernel\nsize is about 10%
 	    smaller with bzip2, in comparison to gzip.\nBzip2 us"...)
     at scripts/kconfig/nconf.gui.c:535
 #7  0x00000000004055b2 in show_help (menu=0x157f9d0)
         at scripts/kconfig/nconf.c:1257
 #8  0x0000000000405897 in conf_choice (menu=0x157f130)
 	    at scripts/kconfig/nconf.c:1321
 #9  0x0000000000405326 in conf (menu=0x157d130) at
 	    scripts/kconfig/nconf.c:1208
 #10 0x00000000004052e8 in conf (menu=0xb434a0) at
 	    scripts/kconfig/nconf.c:1203
 #11 0x0000000000406092 in main (ac=2, av=0x7fff96a93c38)

Cc: Michal Marek <mmarek@suse.cz>
Cc: Nir Tzachar <nir.tzachar@gmail.com>
Signed-off-by: Stephen Boyd <bebarino@gmail.com>
Signed-off-by: Michal Marek <mmarek@suse.cz>