arm64: module: Mark expected switch fall-through

When fall-through warnings was enabled by default the following warnings
was starting to show up:

../arch/arm64/kernel/module.c: In function ‘apply_relocate_add’:
../arch/arm64/kernel/module.c:316:19: warning: this statement may fall
 through [-Wimplicit-fallthrough=]
    overflow_check = false;
    ~~~~~~~~~~~~~~~^~~~~~~
../arch/arm64/kernel/module.c:317:3: note: here
   case R_AARCH64_MOVW_UABS_G0:
   ^~~~
../arch/arm64/kernel/module.c:322:19: warning: this statement may fall
 through [-Wimplicit-fallthrough=]
    overflow_check = false;
    ~~~~~~~~~~~~~~~^~~~~~~
../arch/arm64/kernel/module.c:323:3: note: here
   case R_AARCH64_MOVW_UABS_G1:
   ^~~~

Rework so that the compiler doesn't warn about fall-through.

Fixes: d93512ef0f0e ("Makefile: Globally enable fall-through warning")
Signed-off-by: Anders Roxell <anders.roxell@linaro.org>
Signed-off-by: Will Deacon <will@kernel.org>

arch/arm64/kernel/module.c

@@ -314,18 +314,21 @@ int apply_relocate_add(Elf64_Shdr *sechdrs,
 		/* MOVW instruction relocations. */
 		case R_AARCH64_MOVW_UABS_G0_NC:
 			overflow_check = false;
+			/* Fall through */
 		case R_AARCH64_MOVW_UABS_G0:
 			ovf = reloc_insn_movw(RELOC_OP_ABS, loc, val, 0,
 					      AARCH64_INSN_IMM_MOVKZ);
 			break;
 		case R_AARCH64_MOVW_UABS_G1_NC:
 			overflow_check = false;
+			/* Fall through */
 		case R_AARCH64_MOVW_UABS_G1:
 			ovf = reloc_insn_movw(RELOC_OP_ABS, loc, val, 16,
 					      AARCH64_INSN_IMM_MOVKZ);
 			break;
 		case R_AARCH64_MOVW_UABS_G2_NC:
 			overflow_check = false;
+			/* Fall through */
 		case R_AARCH64_MOVW_UABS_G2:
 			ovf = reloc_insn_movw(RELOC_OP_ABS, loc, val, 32,
 					      AARCH64_INSN_IMM_MOVKZ);
@@ -393,6 +396,7 @@ int apply_relocate_add(Elf64_Shdr *sechdrs,
 			break;
 		case R_AARCH64_ADR_PREL_PG_HI21_NC:
 			overflow_check = false;
+			/* Fall through */
 		case R_AARCH64_ADR_PREL_PG_HI21:
 			ovf = reloc_insn_adrp(me, sechdrs, loc, val);
 			if (ovf && ovf != -ERANGE)