powerpc/spe: Mark expected switch fall-throughs

Mark switch cases where we are expecting to fall through.

Fixes errors such as below, seen with mpc85xx_defconfig:

  arch/powerpc/kernel/align.c: In function 'emulate_spe':
  arch/powerpc/kernel/align.c:178:8: error: this statement may fall through
    ret |= __get_user_inatomic(temp.v[3], p++);
        ^~
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20190730141917.21817-1-mpe@ellerman.id.au

arch/powerpc/kernel/align.c

@@ -176,9 +176,11 @@ static int emulate_spe(struct pt_regs *regs, unsigned int reg,
 			ret |= __get_user_inatomic(temp.v[1], p++);
 			ret |= __get_user_inatomic(temp.v[2], p++);
 			ret |= __get_user_inatomic(temp.v[3], p++);
+			/* fall through */
 		case 4:
 			ret |= __get_user_inatomic(temp.v[4], p++);
 			ret |= __get_user_inatomic(temp.v[5], p++);
+			/* fall through */
 		case 2:
 			ret |= __get_user_inatomic(temp.v[6], p++);
 			ret |= __get_user_inatomic(temp.v[7], p++);
@@ -259,9 +261,11 @@ static int emulate_spe(struct pt_regs *regs, unsigned int reg,
 			ret |= __put_user_inatomic(data.v[1], p++);
 			ret |= __put_user_inatomic(data.v[2], p++);
 			ret |= __put_user_inatomic(data.v[3], p++);
+			/* fall through */
 		case 4:
 			ret |= __put_user_inatomic(data.v[4], p++);
 			ret |= __put_user_inatomic(data.v[5], p++);
+			/* fall through */
 		case 2:
 			ret |= __put_user_inatomic(data.v[6], p++);
 			ret |= __put_user_inatomic(data.v[7], p++);