MIPS/GAS: Cut TLS reloc dead code path in `md_apply_fix'

MIPS/GAS: Cut TLS reloc dead code path in `md_apply_fix'

With code refactoring made in commit b886a2ab0d52 and the addition of
`calculate_reloc' and a separate test for TLS relocs against constants
made there the preexisting fall-through from the TLS reloc switch case
has effectively become a dead execution path.  This is because the call
to `calculate_reloc' present there is only made if `fixP->fx_done' is
true, which can only be the case if `fixP->fx_addsy' is NULL, which in
turn has already triggered the TLS reloc test and made execution break
out of the switch statement.

Remove the fall-through then and reshape code accordingly.

	gas/
	* config/tc-mips.c (md_apply_fix)
	<BFD_RELOC_MIPS16_TLS_TPREL_LO16>: Remove fall-through, adjust
	code accordingly.