Correct the SYNC hint for the release barrier

The MIPS32 manual I have says 0x11 is SYNC_ACQUIRE and 0x12 is
SYNC_RELEASE. The change was an unintentional mistake in commit
60b6b28c21.

Thanks to Spencer Schumann for spotting this.

Change-Id: I16885e4e86e8befa8931733d0b5a54ac9942f176
Reviewed-by: Spencer Schumann <spencer.schumann@echostar.com>
Reviewed-by: Olivier Goffart <ogoffart@woboq.com>
Reviewed-by: Lisandro Damián Nicanor Pérez Meyer <perezmeyer@gmail.com>

src/corelib/arch/qatomic_mips.h

@@ -121,7 +121,7 @@ void QBasicAtomicOps<size>::releaseMemoryFence(const T &) Q_DECL_NOTHROW
 {
     asm volatile (".set push\n"
                   ".set mips32\n"
-                  "sync 0x11\n"
+                  "sync 0x12\n"
                   ".set pop\n" ::: "memory");
 }