MIPS/asm/printk: Fix build failure caused by printk

The commit 3370155 ("printk: Userspace format indexing support")
caused the following build failure:

arch/mips/kernel/genex.o: In function `handle_mcheck_int':
(.text+0x190c): undefined reference to `printk'
arch/mips/kernel/genex.o: In function `handle_reserved_int':
(.text+0x1c8c): undefined reference to `printk'

Fixes: 3370155 ("printk: Userspace format indexing support")
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Suggested-by: Chris Down <chris@chrisdown.name>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/YPbBfdz9srIpI+bb@chrisdown.name

Author: pmladek

arch/mips/include/asm/asm.h

@@ -114,7 +114,7 @@ symbol		=	value
 		.set	push;				\
 		.set	reorder;			\
 		PTR_LA	a0, 8f;				\
-		jal	printk;				\
+		jal	_printk;			\
 		.set	pop;				\
 		TEXT(string)
 #else