Staging: p9auth: fix dependency/build error

Fix p9auth dependency/build failure.  It needs to depend on
CRYPTO.

p9auth.c:(.text+0x107297): undefined reference to `crypto_alloc_base'
p9auth.c:(.text+0x1073d4): undefined reference to `crypto_destroy_tfm'
Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Cc: Ashwin Ganti <ashwin.ganti@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/staging/p9auth/Kconfig

 config PLAN9AUTH
 	tristate "Plan 9 style capability device implementation"
 	default n
+	depends on CRYPTO
 	help
 	  This module implements the Plan 9 style capability device.