Fix ldah being disassembled as ldaexh

2015-12-02  Andre Vieira  <andre.simoesdiasvieira@arm.com>

opcodes/
    * arm-dis.c (arm_opcodes): <ldaexh>: Fix typo...
    <ldah>: ... to this.

gas/testsuite/
    * gas/arm/armv8-a.d: <ldaexh>: Rename mismatched mnemonics ...
    <ldah>: ... to this.