ARM: keystone: fix compilation warning

Fix the following compilation warning:

arch/arm/mach-keystone/keystone.c:74:2: warning: initialization from incompatible pointer type [enabled by default]
arch/arm/mach-keystone/keystone.c:74:2: warning: (near initialization for ‘__mach_desc_KEYSTONE.restart’) [enabled by default]

Signed-off-by: Vincent Stehlé <[e-mail]>
Cc: Robin Holt <[e-mail]>
Cc: Russell King <[e-mail]>
Cc: [e-mail]
Signed-off-by: Olof Johansson <[e-mail]>

arch/arm/mach-keystone/keystone.c

···
 	NULL,
 };
 
-void keystone_restart(char mode, const char *cmd)
+void keystone_restart(enum reboot_mode mode, const char *cmd)
 {
 	u32 val;