ARM: mm: fix alignment handler faults under memory pressure

When the system has high memory pressure, the page containing the
instruction may be paged out.  Using probe_kernel_address() means that
if the page is swapped out, the resulting page fault will not be
handled because page faults are disabled by this function.

Use get_user() to read the instruction instead.

Reported-by: Jing Xiangfeng <jingxiangfeng@huawei.com>
Fixes: b255188f ("ARM: fix scheduling while atomic warning in alignment handling code")
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>