powerpc: Fix typo in breakpoint kgdb code.

Currently we are getting:
arch/powerpc/kernel/kgdb.c: In function 'kgdb_arch_exit':
arch/powerpc/kernel/kgdb.c:492:2: error: '__debugger_breakx_match' undeclared (first use in this function)
arch/powerpc/kernel/kgdb.c:492:2: note: each undeclared identifier is reported only once for each function it appears in

Fix the typo.

Signed-off-by: Michael Neuling <[e-mail]>
Signed-off-by: Benjamin Herrenschmidt <[e-mail]>

arch/powerpc/kernel/kgdb.c

···
 	__debugger_bpt = old__debugger_bpt;
 	__debugger_sstep = old__debugger_sstep;
 	__debugger_iabr_match = old__debugger_iabr_match;
-	__debugger_breakx_match = old__debugger_break_match;
+	__debugger_break_match = old__debugger_break_match;
 	__debugger_fault_handler = old__debugger_fault_handler;
 }