microblaze: Fix sparse warning - sw_exceptions

Function sw_exception is linked with asm code.

Warning log:
CHECK   arch/microblaze/kernel/exceptions.c
arch/microblaze/kernel/exceptions.c:53:6: warning: symbol 'sw_exception' was not declared. Should it be static?

Signed-off-by: Michal Simek <monstr@monstr.eu>
diff --git a/arch/microblaze/kernel/exceptions.c b/arch/microblaze/kernel/exceptions.c
index a7fa6ae7..66fad23 100644
--- a/arch/microblaze/kernel/exceptions.c
+++ b/arch/microblaze/kernel/exceptions.c
@@ -50,7 +50,7 @@
 }
 
 /* for user application debugging */
-void sw_exception(struct pt_regs *regs)
+asmlinkage void sw_exception(struct pt_regs *regs)
 {
 	_exception(SIGTRAP, regs, TRAP_BRKPT, regs->r16);
 	flush_dcache_range(regs->r16, regs->r16 + 0x4);