MIPS: ftrace: Fix the CONFIG_DYNAMIC_FTRACE=n compile

MIPS: ftrace: Fix the CONFIG_DYNAMIC_FTRACE=n compile

arch/mips/kernel/ftrace.c: In function ‘ftrace_get_parent_ra_addr’:
arch/mips/kernel/ftrace.c:212: error: implicit declaration of function ‘in_kernel_space’
arch/mips/kernel/ftrace.c: In function ‘prepare_ftrace_return’:
arch/mips/kernel/ftrace.c:314: error: ‘MCOUNT_OFFSET_INSNS’ undeclared (first use in this function)
arch/mips/kernel/ftrace.c:314: error: (Each undeclared identifier is reported only once
arch/mips/kernel/ftrace.c:314: error: for each function it appears in.)

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
To: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/2634/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>