ARC: asm-offsets: remove duplicate entry

We define 'PT_user_r25' twice in asm-offsets.c
It's not a big issue as we define it to the same value, however
let's fix it.

Signed-off-by: Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>