Arm64: follow-on to PR gas/27217 fix

Arm64: follow-on to PR gas/27217 fix

PR gas/27217

Prior to trying to address PR gas/28888 I noticed anomalies in how
certain insns would / wouldn't be affected in similar ways.

Commit eac4eb8ecb26 ("Fix a problem assembling AArch64 sources when a
relocation is generated against a symbol that has a defined value") had
two copy-and-paste mistakes, passing the wrong type to
aarch64_force_reloc().

It further failed to add placeholder relocation types to that function's
block of case labels leading to a return of 1. While not of interest for
aarch64_force_relocation() (these placeholders are resolved right in
parse_operands()), calls to aarch64_force_reloc() happen before that
resolution would take place.