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 <[e-mail]>
Signed-off-by: Will Deacon <[e-mail]>

arch/arm64/kernel/module.c

···
 		/* 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);
···
 			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)