[ARM] Add curly braces around switch case [NFC]    

My previous commit r304702 introduced a new case into a switch statement.
This case defined a variable but I forgot to add the curly brackets around the
case to limit the scope.

This change puts the curly braces back in so that the next person that adds a
case doesn't get a build failure. Thanks to avieira for the spot.

Differential Revision: https://reviews.llvm.org/D33931

llvm-svn: 304785
diff --git a/llvm/lib/Target/ARM/MCTargetDesc/ARMAsmBackend.cpp b/llvm/lib/Target/ARM/MCTargetDesc/ARMAsmBackend.cpp
index 2ac9b98..d99e9b6 100644
--- a/llvm/lib/Target/ARM/MCTargetDesc/ARMAsmBackend.cpp
+++ b/llvm/lib/Target/ARM/MCTargetDesc/ARMAsmBackend.cpp
@@ -695,7 +695,7 @@
       return 0;
     }
     return Value;
-  case ARM::fixup_t2_so_imm:
+  case ARM::fixup_t2_so_imm: {
     Value = ARM_AM::getT2SOImmVal(Value);
     if ((int64_t)Value < 0) {
       Ctx.reportError(Fixup.getLoc(), "out of range immediate fixup value");
@@ -712,6 +712,7 @@
     EncValue |= (Value & 0xff);
     return swapHalfWords(EncValue, IsLittleEndian);
   }
+  }
 }
 
 void ARMAsmBackend::processFixupValue(const MCAssembler &Asm,