target/hppa: fix do_stdby_e()

target/hppa: fix do_stdby_e()

stdby,e,m was writing data from the wrong half of the register
into memory for cases 0-3.

Fixes: 25460fc5a71 ("target/hppa: Implement STDBY")
Signed-off-by: Sven Schnelle <svens@stackframe.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20240319161921.487080-7-svens@stackframe.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
(cherry picked from commit 518d2f4300e5c50a3e6416fd46e58373781a5267)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>