Fix SBO bit in disassembly mask for ldrah on AArch64.
    
    The disassembly mask for ldarh incorrectly didn't mask out bit 20 which
    is part of the SBO part of the instruction and shouldn't be considered input.
    
    This fixes the wrong bit fixing the disassembly of instructions to
    ldarh and makes the behavior consistent.
    
    opcodes/
    
    	PR binutils/23242
    	* aarch64-tbl.h (ldarh): Fix disassembly mask.
    
    (cherry picked from commit f311ba7ed84d66ae2cd77bd969747d7ab959d866)
    Signed-off-by: Tamar Christina <tamar.christina@arm.com>