hw/sh4/sh7750: Remove forgotten abort() in the MM_ITLB_DATA handler

QEMU currently aborts when the guest writes to the MM_ITLB_DATA register:

 echo "writel 0xf3000000 0x11223344" | \
  ./qemu-system-sh4 -M r2d -display none -accel qtest -qtest stdio
 [I 0.000000] OPENED
 [R +0.004476] writel 0xf3000000 0x11223344
 Aborted                    (core dumped)

Looking at the history of the code, the abort() here has likely just
been forgotten when the register handler had been implemented (it used
to be a reminder about unimplemented functionality initially):

 https://gitlab.com/qemu-project/qemu/-/commit/9f97309a70f12df5f9104f1f

Thus simply remove the abort() now to get rid of the problem.

Resolves: https://gitlab.com/qemu-project/qemu/-/work_items/3420
Signed-off-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-ID: <20260422075429.341409-1-thuth@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>